DOC: Move all docs into en/ subdirectory (#1505)

* DOC: Move all docs into en/ subdirectory

PR #1502 is working on adding a Chinese translation to the docs. In
general, I encouraged this (in #1452) as a path towards getting useful
translated content in the game without requiring a massive
refactor/rearchitecting of everything.

To support this, this takes the first step of moving our docs into an
en/ subdirectory, so that other languages can live alongside. No effort
is made at this time to support or select between alternate languages;
this is a pure-rename refactor.

src/Documentation/doc/en/basic/stockmarket.md

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+# Stock Market
+
+The Stock Market refers to the World Stock Exchange (WSE), through which you can buy and sell stocks in order to make money.
+
+The WSE can be found in the `City` tab, and is accessible in every city.
+
+## Fundamentals
+
+The Stock Market is not as simple as "buy at price X and sell at price Y".
+The following are several fundamental concepts you need to understand about the stock market.
+
+For those that have experience with finance/trading/investing, please be aware that the game's stock market does not function exactly like it does in the real world.
+So these concepts below should seem similar, but won't be exactly the same.
+
+## Positions: Long vs Short
+
+First off, note that _all_ transactions have a flat commission fee, so
+high-frequency trading is not a good strategy.
+
+When making a transaction on the stock market, there are two types of positions: Long and Short.
+A Long position is the typical scenario where you buy a stock and earn a profit if the price of that stock increases.
+Meanwhile, a Short position is the exact opposite.
+
+In a Short position, you borrow shares of a stock to sell and earn a profit if the price of that stock decreases.
+This is also called 'shorting' a stock. The proceeds from the sale are held as
+collateral, called 'margin'. You also have to add additional margin equal to
+the current value of the stock - this is the cost to 'purchase' the short.
+
+When you close a short position, you buy back the shares to pay back the securities loan.
+You then get the margin back, minus whatever was used to repurchase the shares.
+So, your profit is still the change in price times the number of shares.
+Beware that, unlike Long positions which have unlimited upside and limited
+downside, shorts have limited upside and unlimited downside, and selling a
+sufficiently underwater short can cause your money to go negative.
+
+Shorting stocks is not available immediately, and must be unlocked later in the game.
+
+## Forecast & Second-Order Forecast
+
+A stock's forecast is its likelihood of increasing or decreasing in value.
+The forecast is typically represented by its probability of increasing in either a decimal or percentage form.
+For example, a forecast of `70%` means the stock has a `70%` chance of increasing and a `30%` chance of decreasing.
+
+A stock's second-order forecast is the target value that its forecast trends towards.
+For example, if a stock has a forecast of `60%` and a second-order forecast of `70%`, then the stock's forecast should slowly trend towards `70%` over time.
+However, this is determined by RNG so there is a chance that it may never reach `70%`.
+
+Both the forecast and the second-order forecast change over time.
+
+A stock's forecast can be viewed after purchasing Four Sigma (4S) Market Data access.
+This lets you see the forecast info on the Stock Market UI.
+If you also purchase access to the 4S Market Data TIX API, then you can view a stock's forecast using the `getStockForecast` function.
+
+A stock's second-order forecast is always hidden.
+
+## Spread (Bid Price & Ask Price)
+
+The **bid price** is the maximum price at which someone will buy a stock on the stock market.
+
+The **ask price** is the minimum price that a seller is willing to receive for a stock on the stock market
+
+The ask price will always be higher than the bid price (This is because if a seller is willing to receive less than the bid price, that transaction is guaranteed to happen).
+The difference between the bid and ask price is known as the **spread**.
+A stock's "price" will be the average of the bid and ask price.
+
+The bid and ask price are important because these are the prices at which a transaction actually occurs.
+If you purchase a stock in the long position, the cost of your purchase depends on that stock's ask price.
+If you then try to sell that stock (still in the long position), the price at which you sell is the stock's bid price.
+Note that this is reversed for a short position.
+Purchasing a stock in the short position will occur at the stock's bid price, and selling a stock in the short position will occur at the stock's ask price.
+
+## Transactions Influencing Stock Forecast
+
+Buying or selling a large number of shares of a stock will influence that stock's forecast & second-order forecast.
+The forecast is the likelihood that the stock will increase or decrease in price.
+The magnitude of this effect depends on the number of shares being transacted.
+More shares will have a bigger effect.
+
+The effect that transactions have on a stock's second-order forecast is significantly smaller than the effect on its forecast.
+
+## Order Types
+
+There are three different types of orders you can make to buy or sell stocks on the exchange:
+Market Order, Limit Order, and Stop Order.
+
+Limit Orders and Stop Orders are not available immediately, and must be unlocked later in the game.
+
+When you place a Market Order to buy or sell a stock, the order executes immediately at whatever the current price of the stock is.
+For example if you choose to short a stock with 5000 shares using a Market Order, you immediately purchase those 5000 shares in a Short position at whatever the current market price is for that stock.
+
+A Limit Order is an order that only executes under certain conditions.
+A Limit Order is used to buy or sell a stock at a specified price or better.
+For example, lets say you purchased a Long position of 100 shares of some stock at a price of \$10 per share.
+You can place a Limit Order to sell those 100 shares at \$50 or better.
+The Limit Order will execute when the price of the stock reaches a value of \$50 or higher.
+
+A Stop Order is the opposite of a Limit Order.
+It is used to buy or sell a stock at a specified price (before the price gets 'worse').
+For example, lets say you purchased a Short position of 100 shares of some stock at a price of \$100 per share.
+The current price of the stock is \$80 (a profit of \$20 per share).
+You can place a Stop Order to sell the Short position if the stock's price reaches \$90 or higher.
+This can be used to lock in your profits and limit any losses.
+
+Here is a summary of how each order works and when they execute:
+
+**In a LONG Position:**
+
+A Limit Order to buy will execute if the stock's price <= order's price
+
+A Limit Order to sell will execute if the stock's price >= order's price
+
+A Stop Order to buy will execute if the stock's price >= order's price
+
+A Stop Order to sell will execute if the stock's price <= order's price
+
+**In a SHORT Position:**
+
+A Limit Order to buy will execute if the stock's price >= order's price
+
+A Limit Order to sell will execute if the stock's price <= order's price
+
+A Stop Order to buy will execute if the stock's price <= order's price
+
+A Stop Order to sell will execute if the stock's price >= order's price.
+
+## Player Actions Influencing Stocks
+
+It is possible for your actions elsewhere in the game to influence the stock market.
+
+### Hacking
+
+If a server has a corresponding stock (e.g. _foodnstuff_ server -> FoodNStuff stock), then hacking that server can decrease the stock's second-order forecast.
+This causes the corresponding stock's forecast to trend downwards in value over time.
+
+This effect only occurs if you set the stock option to true when calling the `hack` function.
+The chance that hacking a server will cause this effect is based on what percentage of the server's total money you steal.
+
+A single hack will have a minor effect, but continuously hacking a server for lots of money over time will have a noticeable effect in making the stock's forecast trend downwards.
+
+### Growing
+
+If a server has a corresponding stock (e.g. `foodnstuff` server -> FoodNStuff stock), then growing that server's money can increase the stock's second-order forecast.
+This causes the corresponding stock's forecast to trend upwards in value over time.
+
+This effect only occurs if you set the `stock` option to true when calling the `grow` function.
+The chance that growing a server will cause this effect is based on what percentage of the server's total money to add to it.
+
+A single grow operation will have a minor effect, but continuously growing a server for lots of money over time will have a noticeable effect in making the stock's forecast trend upwards.
+
+### Working for a Company
+
+If a [Company](companies.md) has a corresponding stock, then working for that [Company](companies.md) will increase the corresponding stock's second-order forecast.
+This will cause the stock's forecast to (slowly) trend upwards in value over time.
+
+The potency of this effect is based on how effective you are when you work (i.e. it's based on your stats and multipliers).
+
+## Automating the Stock Market
+
+You can write scripts to perform automatic and algorithmic trading on the Stock Market.
+See [TIX API](https://github.com/bitburner-official/bitburner-src/blob/stable/markdown/bitburner.tix.md) for more details.
+
+## Under the Hood
+
+Stock prices are updated every ~6 seconds.
+
+Whether a stock's price moves up or down is random.
+However, stocks have properties that can influence the way their price moves.
+These properties are hidden, although some of them can be made visible by purchasing the Four Sigma (4S) Market Data upgrade.
+Some examples of these properties are:
+
+- Volatility
+- Likelihood of increasing or decreasing (i.e. the stock's forecast)
+- Likelihood of forecast increasing or decreasing (i.e. the stock's second-order forecast)
+- How easily a stock's price/forecast is influenced by transactions
+- Spread percentage
+- Maximum price (not a real maximum, more of a "soft cap")
+
+Each stock has its own unique values for these properties.
+
+## Offline Progression
+
+The Stock Market does not change or process anything while the game has closed.
+However, it does accumulate time when offline.
+This accumulated time allows the stock market to run `50%` faster when the game is opened again.
+This means that stock prices will update every ~4 seconds instead of 6.