Add an execute only prefix to commands `~`

[PoQuatre]

This PR is adding a way to hide commands from tab completion but still allow said command's execution, by doing this, it fixes issue #12.

Example usage

groups:
  default:
    commands:
    - rules
    - ~cmi
    - ~cmil

This will only show the /rules command in the tab completion, but the usage of /cmi and /cmil is still allowed

[YouHaveTrouble]

Denying this. CW was designed to be dead simple "I can see it - I can use it". This not only complicating things, but also would promote bad practice and unexpected behavior.