raylib was using `stb_perlin.h` library to generate perlin noise, it seems that recently this library has been flagged as it could be infringing some algorythm patent. For security, it has been removed from raylib.
Namely:
- GenImageHorizontalV
- GenImageHorizontalH
- GenImageChecked
- GenImageWhiteNoise
- GenImageCellular
The gradient implementation may be a bit naive, for example it doesn't do any gamma correction.