Added support for closing the current window with Alt+F4
Added better support for ALT+F4

Centralized the focus assignment

Added _NET_ACTIVE_WINDOW and WM_STATE elements
Added cache for window data

Captures the keys with all modifiers

Only closes non-dock windows

Only set focus on non-dock windows
Now CLOSE_WINDOW and SET_FOCUS uses the window cache

Fixed a little memory leak
Added support for cicling between same-app windows (Ctrl+TAB) and between apps windows (Alt+TAB)

Fixed another memory leak (thanks, valgrind!!!!)