Fix missing report IDs in feature reports

As it is the case for input reports, the ID has to be sent for feature
reports when a device has multiple reports implemented.

Signed-off-by: Bert van Hall <bert.vanhall@avionic-design.de>
Merge pull request #28 from The-42/fix-feature-id

Fix missing report IDs for HID device class GetReport request responses (thanks to Bert van Hall).
Update documentation for HID report ID fix.