REF: added options in sct_straighten_spinalcord
REF: added options in sct_straighten_spinalcord

Former-commit-id: 71401ae1d538f06e57cc6ef1608382d3c8cb7aa8 [formerly d1f3569479abe9c795e3b58c7865c55dbaeb9d4d]
Former-commit-id: 9cbe1e457b7cdbdff8796aa4b73c9fc0be7b3cca
Former-commit-id: bc1c9bb6774dc75c35bec8220c1182ac8834d9d3
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox