Support more scaling filters such as Bicubic or Lanczos

[Sukid]

I just thought it would be cool to have a few more scaling filters available, like bicubic and lanczos. Bicubic has looked a bit nicer for downscaling in my experience!

[Ferdi265]

Scaling is currently implemented via the OpenGL GL_TEXTURE_MIN_FILTER/GL_TEXTURE_MAG_FILTER texture parameter options.

Supporting other scaling filters would require actually implementing them manually (and I have no experience implementing such algorithms) because OpenGL does not provide them as far as I know.

I'll gladly accept a PR that adds this, but probably won't implement this myself in the near future (at least until I find enough time to look at how texture filtering actually works)