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.

Skipped `args.merge!` since this way I take profit of the "sanitization" (`to_s`) done at `<<`'s implementation.