Changed HWB board driver to Buttons driver, to allow for the support of future boards with more than one mounted GPIO button.

Fixed incorrect HID interface class and subclass values in the Mouse and KeyboardMouse demos (thanks to Brian Dickman).

Capitolised the "Descriptor_Search" and "Descriptor_Search_Comp" prefixes of the values in the DSearch_Return_ErrorCodes_t and DSearch_Comp_Return_ErrorCodes_t enums.

Minor documentation improvements.