* 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.
* Remove all Makefiles from the keyboards directory.
* update keymaps added in the last 8 days
* Ignore keyboard/keymap makefiles
* update hand_wire to reflect our new Makefile-less reality
* Update the make guide to reflect the new reality
* move planck keymap options to rules.mk
* update planck keymaps 4real
* trigger travis
* add back build_keyboard.mk
* restore changes to build_keyboard
