Improve the bind[] option to accept pointer buttons.

Improve the bind[] option to accept pointer buttons.
Buttons are specified as Button<n> (case sensitive) where n is 1 to 255.

	Example:
	bind[move] = MOD+Button8

Existing pointer actions are now available for bind[]:
	focus - Focus window/region under pointer.
	move - Move window with pointer while binding is pressed.
	resize - Resize window with pointer while binding is pressed.
	resize_centered - Same as resize but keep window centered.

	Defaults:
	bind[focus] = ANYMOD+REPLAY+Button1
	bind[move] = MOD+Button1
	bind[resize] = MOD+Button3
	bind[resize_centered] = MOD+Shift+Button3

Button binds can be unbound the same as key binds:

	Example:
	bind[] = MOD+Button1 # unbind default move binding.

Add new special bind arguments:
	ANYMOD
	Binds all modifier combinations not handled by another binding.

	REPLAY
	Allows other programs to receive press/release events for bind.
	Unavailable for move, resize and resize_centered.