Add example to evaluate sky shader on CPU

[repi]

Adds a new example that shows how to compile and evaluate a simple fragment shader (our sky shader) directly on the CPU.

For this specific shader as it doesn't use any resources it is very easy as one can just call the fragment shader function manually, later for standard shaders with resource bindings this will be much harder, but maybe still useful to test parts of shaders or reuse some functionality.

Right now it also just works for the current temp math functions that use core intrinsic, as all of those are available obviously on the CPU also, later when we start introducing GPU & SPIRV specific intrinsics (#81), this approach won't work, and then we will want to use a higher-level math layer in the shaders for the math instructions (glam: #134) so they can be mapped to the right available target intrinsic.

To make the example very simple, slim and cross-platform, this example uses the minifb crate to drive the Window. Could switch to something else later though but it is very basic.

[khyperia]

this is super cool, and impressively simple!

later when we start introducing GPU & SPIRV specific intrinsics (#81), this approach won't work

It should work, I plan on implementing it in a way where it should work.

[Jasper-Bekkers]

I love that we can do this :-)

[repi]

Ah some cargo-deny stuff to fix with the minifb dependency

[repi]

@Mergifyio rebase

[mergify]

Command rebase: success

Branch has been successfully rebased