REF: improve usage generation of the parser
REF: improve usage generation of the parser

Former-commit-id: 3b873a2e26795f588b6da72779c3169af6c30977
Former-commit-id: a892b5bc956c8bec0fc87e18f7a56239256cd4a5
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox