Allow binding callbacks to raw key input events
Re-order, refactor, and update comments on InputDispatcher
Give Mesh nice String() formatting
Make default Mesh and Material explicit, consolidate mesh loading

Outside of improving the logging output of loading Meshes, I like the
feel of explicitly checking for unset values and putting the default in
place manually.
Update comments, add some logging, move code around for readability
Refactor MarchingCubes and add tests and benchmarks

First of what will probably be multiple attempts at making this code
somewhat understandable. It's still very mathy but the individual
sections now stand out and can be attacked individually.