test: add test for extracting the right slot values on startup

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Sync the initial slot state from the device

libevdev_get_slot_value() needs to return the correct value from the outset.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
README: Drop the details, refer to documentation instead

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

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Add a simple example to the documentation

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