OPT: msct_parser.py now generate usage based on the option list
OPT: msct_parser.py now generate usage based on the option list

Former-commit-id: 17eba5ae92c87d43ee180f233b14b703f18f4e45 [formerly 5ce9818aeb00a9d07aff4f24e39b11840af617c0]
Former-commit-id: 0d794db4a5197825e25c1ce02f56ed25ec06add6
Former-commit-id: 33914cd9ea35a9854a2911208380a994a228087d
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox