Async refactor

[randomPoison]

Refactor the renderer to user fibers in a manner similar to how we refactored the engine core. OpenGL still can handle running in parallel, but at the least we can make the renderer thread-safe to a degree and make it better integrate with the rest of the engine.

[randomPoison]

The biggest thing that could be improved here would be to move the resource handle management into the renderer. Currently the engine does a lot of work to turn the IDs generated by polygon into unique handles that can be used safely in a multi-threaded context. This work could be done by polygon directly, which would likely simplify the engine's code and bring some clarity as to other ways for polygon to be parallelized.