Prevent the options documentation from exploding in size.

Makes the options page a bit more readable.

Including the new #pragma GLSL macro

This marks the first time the entire syntax was documented outside of
the source code as reference. Hooray!

Slightly more readable. I think.

Using `mkdocs` + `material` theme because it was the nicest-looking
thing that I found with a few minutes of googling for alternatives.

Here's hoping I don't regret that decision.