Fix some coding style inconsistencies

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Allow initial device configuration after receiving DEVICE_ADDED event

By specifying that a device will not be read until the next time the
user calls libinput_dispatch(), if data is available, it will allow for
setting up initial configuration, such as tap button, output screen
size, acceleration parameters, etc.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Document the LIBINPUT_EVENT_NONE event type

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>