Added support for multi-parameter options

Parameters with more than one option, like `-morphology` or `-annotate` are not supported anymore, are they? Had to use `<<` to add the extra options that are not as tidy, as in:

      cmd.morphology "Close:1"
      cmd << "Disk:8.3"

This is a proposed implementation if you would like to re-implement that feature.

Not 100% sure of this name, but looks like you're following `Hash` api. Also not sure if it has any sense for this to be public, though it doesn't hurt, right?