Userspace input device daemon
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- allow to read keymap config from a file instead of compiling it in

- improve combo key handling
  - sticky keys entry mode?

- add various modal modes:
  - show modal hints on the display 
    - write to linux console framebuffer directly
    - run a generic process/script (eg. to show mode in i3 status bar)

Modes:

- navigation mode arrows work as arrows without holding Fn key, holding
  Fn key inverts the meaning to primary (so Fn+Up types a 'dot')
- sticky Fn mode (all keys act as if Fn is being held)
- sticky keys mode (build a multi-key shortcut gradually, without having to
  hold multiple keys at once)
- ???

