* Remove unused UNICODE(n) macro, update docs
* Add note about max length of unicode_map to docs
* QK_UNICODE_MAP → QK_UNICODEMAP
* Refactor process_unicode_map
* process_unicode_map → process_unicodemap
This is done for consistency: UNICODEMAP is the method (hence UNICODEMAP_ENABLE, process_unicodemap), whereas unicode_map is the mapping table itself.
* Update references and ordering in docs/understanding_qmk
* Add additional note to docs/understanding_qmk
* &unicode_map[index] → unicode_map + index
This avoids the issue of the compiler sometimes complaining about the array index being out of range
* Update docs/getting_started_make_guide
* Update method sections in docs/feature_unicode
* 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.
* add process_terminal() and update links to other functions
* convert links to permalinks and add a few missing process_* functions
* update links in main text as well
