* Remove chording as it is not documented, not used, and needs work.
* Make Leader Key an optional feature.
* Switch from `PREVENT_STUCK_MODIFIERS` to `STRICT_LAYER_RELEASE`
* Remove `#define PREVENT_STUCK_MODIFIERS` from keymaps.
* Initial K-Type support
* Copy PJRC_TEENSY_3_1 to work around watchdog issues
* K-Type: Remove bootloader offset in rules.mk
* Ensure matrix and scan quantum functions are called when needed
This is porting a fix from f5422a70b6