exact: Inline trivial predicates
exact: Add an incircle test
exact: Add 1% slack around the quantized box for sentinel purposes

This will be useful for Delaunay.
HalfedgeMesh: Test and fix split_face, and add common_halfedge
debug.h: Mark error functions cold
HalfedgeMesh: Add an extremely restricted form of deletion

In its current form, this is basically only usable for removing
sentinels in Delaunay triangulation.
HalfedgeMesh: Add "undirected" edge ids
uint128: Add str for __int128_t (gcc only at the moment)

We'll need a custom int128_t class analogous to uint128_t before it is
portable.  int128_t will be needed by the simulation of simplicity code.
exact: Implement randomized incremental Delaunay triangulation

At the moment, we're an order of magnitude slower than CGAL.
exact: Remove interval filter step

This speeds up ./test_exact -b from 11.8223 s to 10.1608 s.
exact: Store quantized points as integers rather than floats

This speeds up ./test_exact -b from 10.1608 s to 9.4994 s.
exact: Remove verification steps from Delaunay benchmark

This speeds up ./test_exact -b from 9.4994 s to 6.4583 s.
exact/delaunay: Refactor predicates into sentinel/nonsentinel versions

This makes no significant different to timings, but I like it better.
exact/test_exact:.py: Add a -c option to control cgal comparison
exact/delaunay-test: Add a Delaunay animation script
delaunay: Check for interrupts
exact: Add some more modes to Delaunay tests
vector/__init__.py: Support 2D vectors in cross