Fixes warnings [#61] by disabling unused field warnings for two structures in
HidProtocol. These fields aren't currently used by OpenTK but the stuctures are
used in native marshalling so must match the documented structures perfectly.
Due to the way we segregate axes from buttons, the easiest approach is
to retrieve the current button state via HidP_GetUsages().
Axes, buttons and hats are now allocated sequentially based on their
order of appearance in the device capability reports.
Marked arrays with [In] and [Out] as required. Fixes issues with
axis/button capabilities returning empty results.
Added bindings for link collection node transversal.