Automatically detect Xkb at run-time.

Uses XGetKeyboardMapping as a fallback.  Fixes #282.
Cleanup of XKB detection code.
Cleaned up shared key repeat detection.
Fixed broken key repeat detection.
Fixed glfwShowWindow restoring maximized windows.

Fixes #264.
Comment fix.
Call platform API directly where possible.
Fixed possible use of invalid HWND.
Removed deprecated Doxygen options.
Fixed typo in transition guide.
Fixed release of get rule objects.

Partial revert of b4c03b992c.

Fixes #262.
Fixed leaks of joystick mutable arrays.
Start reopen test in fullscreen.
Merge pull request #306 from SephiRok/patch-1

Start reopen test in fullscreen.
Made X11 Unicode table const.
Updated comments on global variables.
Removed uses of GLU in tests.
Only generate Doxyfile if generating docs.

Fixes #307.
Formatting.
Fixed modifier key events being lost.