Compute Shaders

[heyx3]

1. Learn about OpenGL compute shaders, in particular how they're different from rendering shaders in terms of GLSL syntax and draw calls.

2. If possible, implement compute shaders as an alternative mode of Program. Making a whole new type of resource would be a pain, for example all the uniform-setting functions would have to be rewritten, so it should be avoided unless absolutely necessary.

3. Add functions to dispatch a compute shader, similar to GL.render_mesh().

[heyx3]

Compute shaders are added! With unit tests showing them modifying buffers correctly. However, I still need to fix "Image Views" so textures can be writable as well.