Added Xpanda includes, and other small changes

There’s this wonderful tool called Xpanda which is useful for sharing code between shaders (as well as making them cross-compatible between GLSL ES and HLSL). The appeal for something like this should be obvious. It’s not difficult to change the code to conform to Xpanda’s cross-platform formatting requirements, but just because why not I added files for that. It’s $2, although admittedly if one was working on something where this was needed, one would rather just do it themselves and save the $2.

Other than that I’ve made some other adjustments:

• There was an extra color vec4 in the cluck fragment lighting shader. This isn’t usually a problem, at least on Windows, but since I recommended a 36-byte vertex format and it’s usually best to not have the vertex format and shader attributes mismatched I got rid of it.

• Got rid of the GPU alpha test overrides in favor of just getting the values directly, since you can do that in GameMaker and it’s way less work.

Probably won’t make any other changes to this after now.