* 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.
* Refresh & improve leader documentation page
- register_code/unregister_code are not the recommanded way to do macro.
- Provide some details I wish I had found when first used the leader
functionality.
* Add old way to use macro.
