Meshing

[unexcellent]

Create a meshing algorithm for rendering with texture support based on #15.
I mostly copied the code from #15 but made the data structure more native to anvil and simplified the tests.
Todos before merging:

• test non-trivial cases (like rounded faces)
• implement meshing for part
• resolve clippy warnings

[gmorenz]

To address your question on the other thread, yes: up to the inline comments (particularly normals and winding order) this seems fine to me.