Implement commands

[soenkehahn]

It should be possible to implement commands using sumtypes.

data GitOptions
  = Push {
    force :: Bool
  }
  | Fetch {
    branch :: Maybe String
  }

It's a bit tricky to get global options right in that case, but I think it should be doable.

[proger]

:+1: looking forward to it

[fisx]

me too :)