Overhaul USB HID for Leonardo and Micro

This pull request includes the features from pull request 1488 and pull request 1391. I've somewhat overhauled the code to better match the surrounding code and a few features.

I've also added code examples for the less discoverable features.

If this pull request isn't "right" yet, I'd love feedback so I can improve it.
Consumer Control and System Control Descriptors can be shrinked down a lot more and be even more flexible in its use.
https://github.com/NicoHood/HID/blob/402efb58c19e187ae8b6f11d424db4c50fd8f173/HID.cpp#L160-L195