Make BooleanValidator accept bytes too besides int

Previously, only the first parameter byte can be read or written. After this
patch, it is possible to select/write more bytes by specifying a mask of type
bytes with the appropriate length.
Support FN keys swap for K800
Add K710 with FN key swap support (pwr/Solaar#18)

The K710 keyboard is (according to the issue reporter) part of a MK710 combo
(which also contains a M705 mouse). Observing a succesful 07 register read,
I think that it is a HID++ 1.0 device too that uses the same register for FN
key swapping as K800.
Merge pull request #24 from Lekensteyn/hid10-fnkey

Add FN key swap support for K800 (and presumably K710)