Blmath

- Remove reliance on baiji for a single test asset
- blmath.numerics.linalg.cholmod working in python 3
- Set up tox to run tests locally across python versions
- Removed conditional import from OpenDR (and all references to OpenDR)

- Merge Metabolize fork back into [original repo at its new home][repo].

[repo]: https://github.com/lace/blmath

- TriNormalsScaled: Fix for Python 3

- Update for Python 3.

- Move Plane.polyline_xsection to Polyline.intersect_plane.
- Polyline: Add `reindexed()` method.
- Polyline: Add `cut_by_plane()` method.

- Plane.polyline_xsection: Add `ret_edge_indices` parameter
- Polyline: Add convenience attributes `segments` and `segment_vectors`
- Polyline: Add `flip()` method.