Support Substituting Custom Layers

[manna-harbour]

Support easy customising of layers by allowing substitute layer data to be defined outside the keymap.

• [x] Define all alternative layer data for easy copying. See miryoku_alternatives.h
• [x] Define layer data selected by alternative layout options for easy substitution. See miryoku_layer.h
• [x] Allow layer data to be overridden. See miryoku_layer.h
• [x] Test overriding layer data. E.g. copy the definition of MIRYOKU_ALTERNATIVES_BASE_COLEMAKDHK from miryoku_alternatives.h to the appropriate file and change macro name to MIRYOKU_LAYER_BASE.
  • [x] Miryoku QMK
  • [x] Miryoku ZMK
  • [x] Miryoku KMonad
• [x] Add custom_config.h to all implementations and change workflows to append instead of overwrite
• [x] Add documentation

[manna-harbour]

Support for substituting layers and per layer mappings has been added. See https://github.com/manna-harbour/miryoku/discussions/85.