* Update default Nyquist revision
* LED slave fix
* Sync changes from lets_split
* Add needed check for debouncing
* Remove line that was setting PD2 pin and interfering with use of that pin
* Add backlight key to keymap
The let's split code used delays in its debouncing algorithm which
increases input latency. This commit copies and adapts the code from
`quantum/matrix.c` to lets_split's `matrix.c`.