Three test devices provided:
btn0 .... Provides BTN_0, BTN_1, BTN_2 instead of BTN_LEFT, BTN_MIDDLE,
BTN_RIGHT.
abs ..... Provdes x/y absolute axes, jumps between 100/100 and 120/120.
absrel .. Provides relative x/y axes and absolute x/y axes at the same time.
Signed-off-by: Peter Hutterer <peter.hutterer@redhat.com>