Compute Shader support

[maluoi]

Because GPUs are fast at computing!

[ib00]

What's the current status of compute (especially on Vulkan)?

[maluoi]

I do still have some work to wrap up compute shaders, but it's working in DirectX + OpenGL already. You can see the current example in the compute_shader branch.

I don't consider it complete, largely because I haven't yet had the opportunity to battle-test it in StereoKit. I'm expecting there'll probably be some additions or revisions when I do that.

Also, sk_gpu doesn't exactly have Vulkan support. There's some dead Vulkan code around, but I never had the time to complete it.