Add Tap-Only Layer

[manna-harbour]

Add a toggleable copy of the base layer without dual function keys for use with games (and applications with similar needs such as KMonad).

• A copy of the base layer but with only the tap keycodes from the tap holds
• Only immediate press / release behaviour, no delays
• Additional QWERTY version for non-QWERTY base layers, for games that don't support remapping?
• Auto shift also needs to be disabled
  • QMK https://beta.docs.qmk.fm/using-qmk/software-features/feature_auto_shift
    • Can be disabled in QMK with KC_ASON / KC_ASOFF / KC_ASTG and no AUTO_SHIFT_NO_SETUP. Should add to keyboard control layer anyway.
    • Auto disable / enable on layer change with custom code
  • ZMK has no auto shift yet. Add fake auto shift via tap hold but leave off for tap-only layer
  • KMonad has no auto shift yet. Using fake auto shift via tap hold but can leave off for tap-only layer. Or just exit and use raw keyboard but might need faster / smoother switching.
• Use superset mapping, map all extra keys to unique keys for rebinding
  • Support overriding layout macros from config file
  • Add default for this layer to common mappings
• Activation:
  • Activate from unused keycode similar to current reset. Won't be able to return to normal mode without hardware reset.
  • Activate / deactivate from unused extra key in subset mapping. Not available on 36 key boards.

[manna-harbour]

A tap only layer has been added. See https://github.com/manna-harbour/miryoku/tree/master/docs/reference#additional-features.
Layers can be added and substituted, and mappings can be substituted for all layers or per layer. See #85.

[manna-harbour]

Tap layer and other Additional Features now require a double tap to activate to prevent accidental activation.