USB HID support

[thejpster]

Adds a USB Keyboard type which can handle USB HID frames from a Keyboard in Boot Mode.

Builds on #52 so merge that first.

[eldruin]

Thank you! Could you have a look at the conflicts?

[thejpster]

Yeah, just needs a rebase.

[thejpster]

Added a test case using reports captured from my actual keyboard - works as expected. Also added a CHANGELOG entry.

[thejpster]

Force pushed with fixed formatting

[thejpster]

It appears USB HID keyboards don't send repeated reports when a key is held down - unlike PS/2 keyboards. Therefore we'll need some way of submitting a 'blank' report, which causes every key currently pressed to get emitted again. But you'll want to time that right because if the timer fires immediately after a key is pressed, you'll get a double character that you don't want. Maybe we'll end up needing a HashMap of (Keycode, TimeSincePressed).

Or just not worry about it. On a modern macOS machine, it doesn't even do repeated characters when a key is held - it pops up an accented character picker instead.

[eldruin]

Interesting. Do you want to do more changes about that here or should this be merged as-is?

[thejpster]

Oh this is fine as-is. Typematic repeats can be a separate thing.

[eldruin]

Thank you!