Fix float stability in orthogonal_vector

[ffreyer]

Fixes #251

Switched the generic orthogonal_vector to

$$\sum_i (q_i - q_1) \times (q_{i+1} - q_1) = \sum_i q_i \times q_{i+1} - q_0 \times q_{i+1} - q_i \times q_0$$

which is equivalent to the previous formula as the last two terms cancel. (Swapping the order of cross product inputs introduces a - which allows one term to cancel the other over the full summation.) (The summation skips the last iteration as q_i+1 - q_1 = q_1 - q_1 doesn't contribute.)

Also extended the types for the fast path so it's hit by default for triangle meshes again

All the failing triangles from #251 removed subtractions from the cross product. I added a few of these as tests, as well as one which doesn't remove subtractions. I also added another sanity check for faces with more than 4 vertices (verified on master) as I was getting confused about what length to expect.