REF: sct_compute_mtr: added parser
REF: sct_compute_mtr: added parser

Former-commit-id: 222984ea10335ae1c7c84044a969b8b34adf026e
Former-commit-id: d85f687278b2ac07f1888198cf1ff83d642fbe98
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox