Homology

[videlec]

• [x] implement homology for FatGraph and generic computation of spin parity
• [x] deprecate RibbonGraph and use FatGraph instead
• [ ] implement relative homology (to subset of vertices) and excision (relative to faces) $H_1(S \ V, F; R)$
• [ ] implement (relative) co-homology (using the cotree rather than the tree)
• [ ] duality

Checklist

• [x] Added an entry in doc/news/.
• [x] Added a test for this change.