Add a code-based name lookup function

Add a code-based name lookup function

Two new function pairs:
	libevdev_event_code_from_code_name()
	libevdev_event_type_from_code_name()

	libevdev_event_code_from_code_name_n()
	libevdev_event_type_from_code_name_n()

These functions look up event codes/types by the name of the event code only,
removing the need to figure out what event type an event code has. So if all
you have is "BTN_TOUCH", you can now look up the type and code for that,
without having to check the prefix yourself to guess at the type.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>