feat: Caps_Lock binding available

[fxliang]

• ability to use Caps_Lock in key_binder/bindings

example to binding Caps_Lock to 4 when has_menu, to select the 4th candidate

patch:
  # ensure key_binder is processed before ascii_composer
  engine/processors/@before 0: key_binder
  key_binder/bindings/+:
    # Caps_Lock selecting 4
    - { accept: Caps_Lock, send: 4, when: has_menu} 
    - { accept: Release+Caps_Lock, send: Release+4, when: has_menu}