destroy function for renderparams
annotate that the error branches are unlikely
correct some LICENSE info and add attribution
threedee-simd: fix some gcc const warnings
support sRGB textures (part 1)

It's not supported from outside of texture.c yet,
but now images in sRGB format are supported. Which
is the start of any gamma-correct rendering pipeline.

Code gleaned from the mio project (on github).
refactor resizing, fix warnings, cleanup