Use a pre-compiled shaderc

[parasyte]

Building pixels requires cmake, Python, and a bunch of non-rusty tools. It also makes the initial compilation take about 10 minutes on my recent laptop.

shaderc is one of the heaviest dependencies right now. There are a few "manual hacks" that you can try to link against a precompiled shaderc, but we need a real solution. See: https://github.com/google/shaderc-rs#setup

Until rust-gamedev/wg#23 comes to fruition, we might be able to patch shaderc-rs, but we would need a source of pre-compiled libs for all major platforms.

[parasyte]

I'm just going to go the simple route and pre-compile the shaders to SPIR-V, which will live in the repo alongside the shader source code. Any time the shaders need to be changed (I don't anticipate that happening often) they will need to be recompiled to SPIR-V out-of-band. E.g. cargo will not compile the shaders.

This removes a very large burden, so the tradeoff is worth it for right now.