Created raylib input system (markdown)

raylib-input-system.md

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+raylib input system basically uses an event polling mechanism, centralized on raylib [core module](https://github.com/raysan5/raylib/blob/master/src/core.c).
+
+At the end of the game loop, `EndDrawing()` function is called. This function calls `SwapBuffers()` and `PollInputEvents()`, multiple input devices are scanned at that moment and states are reqistered.
+
+Depending on the platform, input events are managed using different mechanisms. 
+
+Default supported input systems are: `KEYBOARD`, `MOUSE`, `GAMEPAD`, `TOUCH` 
+
+PLATFORM_DESKTOP
+---------------------
+On this platform GLFW3 library ([rglfw](https://github.com/raysan5/raylib/blob/master/src/rglfw.c)) is used for input management. Events polling is done using `glfwPollEvents()`.
+
+Input | Library | Details
+:---: | :---: | ---
+KEYBOARD | GLFW3 | Values are registered through callbacks `KeyCallback()`, `CharCallback()`
+MOUSE | GLFW3 | Values are registered through callbacks `MouseButtonCallback()`, `MouseCursorPosCallback()`, `ScrollCallback()`
+GAMEPAD | GLFW3 | Values registered by (no-callbacks): `glfwJoystickPresent()`, `glfwGetJoystickButtons()`, `glfwGetJoystickAxes()` *NOTE: Those functions do not require `glfwPollEvents()`*
+TOUCH | - | Not available by default. Mouse clicks are mapped to touch events using gestures API.
+ 
+PLATFORM_WEB
+--------------
+Some of the inputs in this platform are directly using GLFW3 because the library has been partially [ported to emscripten](https://github.com/emscripten-core/emscripten/blob/incoming/src/library_glfw.js). Despite that, gamepad and touch inputs are directly managed using emscripten API.
+
+Input | Library | Details
+:---: | :---: | ---
+KEYBOARD | GLFW3 | Same as `PLATFOM_DESKTOP`, uses GLFW3 JS implementation
+MOUSE | GLFW3 | Same as `PLATFOM_DESKTOP`, uses GLFW3 JS implementation
+GAMEPAD | Emscripten | Using emscripten gamepad API: `EmscriptenGamepadCallback()`
+TOUCH | Emscripten | Using emscripten touch API: `EmscriptenTouchCallback()`
+
+PLATFORM_ANDROID
+------------------
+Android NDK provides its own events polling system: `ALooper_pollAll()`, called on `PollInputEvents()`.
+
+Using `AndroidInputCallback()`, all inputs can be later processed. Currently only some inputs are processed but additional inputs could be processed
+
+Input | Library | Details
+:---: | :---: | ---
+KEYBOARD | Android NDK | Keys registered on `AndroidInputCallback()`
+MOUSE | - | Mouse inputs are actually mapped with TOUCH input
+GAMEPAD | Android NDK | Support *partially* implemented on `AndroidInputCallback()`
+TOUCH | Android NDK | Touch points registered on `AndroidInputCallback()`
+
+PLATFORM_RPI
+-------------
+Probably this platform inputs polling is the most complex one. Some input events are polled by multiple secondary threads.
+
+Keyboard polling is a special case, it can use directly `stdin` inputs to read keycodes. In that case, `stdin` is being reconfigured for ASCII chars reading and reseted at the end of the program... This approach presents several problems like a standard input lose if program is not closed properly but it does not require `X.org` libraries or superuser rights... Second option is being implemented to avoid `stdin` usage.
+
+Input | Library | Details
+:---: | :---: | ---
+KEYBOARD (1) | - | `stdin` is remapped to read keys using: `InitKeyboard()`, `ProcessKeyboard()`, `RestoreKeyboard()`
+KEYBOARD (2) | libevdev | Using standard `input_event` to read events from input device
+MOUSE | libevdev | **Threaded**: `InitMouse()` -> `EventThreadSpawn()` -> `EventThread()`, uses `input_event`
+GAMEPAD | joystick.h | **Threaded**: `InitGamepad()` -> `GamepadThread()`, uses `js_event`
+TOUCH | libevdev | *Share `MOUSE` implementation*
+
+Probably inputs could be further improved in all platforms, specially TOUCH inputs support and mapping with MOUSE.