hid10: document notifications better

See [registers.txt][1] for 'keyboard_backlight'. The behavior of
keyboard_sleep_raw and keyboard_multimedia_raw is described at
[keyboard.txt][2].

 [1]: https://git.lekensteyn.nl/ltunify/tree/registers.txt
 [2]: https://git.lekensteyn.nl/ltunify/tree/keyboard.txt
hid10: Formatting and re-order NOTIFICATION_FLAGs

Align values for easier reading the numeric values of NOTIFICATION_FLAGs.  To
maintain consistency in the ordering of the values, swap keyboard_backlight with
keyboard_present.
hid10: update flags description for notifications

The Logitech HID++ 1.0 documentation actually names the fields for devices and
receiver. Clarify that and explain why enabling all of the bits is a bad idea.
Merge pull request #48 from Lekensteyn/doc-updates

Doc updates for HID++ 1.0 notifications