NEW: new function to segment the spinal cord
NEW: new function to segment the spinal cord

Former-commit-id: 1cd6b5abfb0afd6b7c72dd48dd446213073c196a
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox