Provide abstractions for geometric primitives like translations and rotations.

[olson-sean-k]

Theon should probably provide abstractions of foundational geometric primitives like translations, rotations, isometries, etc. that are built from the scalars, points, vectors, and matrices that are already abstracted. Such types would be analogous to similar types provided by some mathematics crates like nalgebra, but generalized to work with various implementations. This could lower the barrier to remaining agnostic to specific crates in library code. See the pictor support crate, for example.

Tangent: Plexus is using Theon to provide computational geometry APIs. I'm still not sure if this would be a good idea (see this issue), but it may be worth considering if the polygonal primitives in Plexus should still migrate into Theon. 🤷