Basic shader bindings

[turnerdev]

Bindings to load shaders and set common uniform types.

Took some inspiration from this fork, though with a different approach to setting shader values ((set-shader-value shader loc-index [1 2] :vec2) vs (set-shader-value-vec2 shader uniform-name [1 2])). Not sure which implementation is considered more idiomatic?

[ianthehenry]

I think your implementation is the correct one. I didn't know anything about Janet when I wrote that originally :)