Redesign CLI options for enabling/disabling conversions with opt-in/opt-out conversions in mind

[yujinakayama]

Opt-in conversions

• Conversion from obj.stub(:message => value) to allow(obj).to receive(:message).and_return(value)
  • Currently using an ad-hoc option -t/--convert-stub-with-hash.
• Conversion to non-monkey-patch describe (Support conversion to non-monkey-patch #describe #22)
  • Not yet implemented but probably this should be opt-in conversion.
• Conversion of hook scope names (Consider supporting conversion of hook scope names #53)
  • Not yet implemented but probably this should be opt-in conversion.