make keyboard work, also include keycode display in 2nd boot

There was 2 bugs in the USB keyboard handling. Now events are sent OK, also modifiers keypress events
are set.

A gamepad emulation funciton which can parse events and produce Gamepad keypressed has been added.

2nd bootloader has been updated to use it and display pressed/released keys
Merge branch 'master' of https://github.com/makapuf/bitbox