Input: MT - Include win8 support

The newly released HID protocol for win8 multitouch devices is capable
of transmitting more information about each touch. In particular, it
includes details useful for touch alignment. This patch completes the
MT protocol with the ABS_MT_TOOL_X/Y events, and documents how to map
win8 devices.

Cc: Stephane Chatty <chatty@enac.fr>
Cc: Benjamin Tissoires <benjamin.tissoires@enac.fr>
Cc: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>