gfxutil: cache opened Shaders/Textures to aide anti-readers.

[slimsag]

There are those anti-readers whom will not read the documentation but rather copy+paste example code in an effort to construct their games.

The downside to this is that they often end up creating several hundred shader/texture objects which is incredibly slow.

If the gfxutil.OpenShader and gfxutil.OpenTexture utility functions used a cache and returned the same shader/texture object in the event that the user specifies the same path, we could aid this specific case.

[slimsag]

Today and yesterday I had the need to reload a shader I'd opened via gfxutil.OpenShader for development (I just bound the R key to perform reloading).

Of course, the shader was cached so I can't use gfxutil.OpenShader anymore. Then we have a few options:

• Add something to clear the cache (gfxutil.ReopenShader).
• Check the last-modified date on the file.
• Revert the change.

I want the utility package to be simple, not a full-blown asset management package. For this reason I am opting for no. 3.