Fixed a grammatical error by removing "are" to change `... but some are have multiple purposes ...` to `... but some have multiple purposes ...` in `textures/textures_image_generation`
* Add GenImageGradientSquare to allow square gradients
* Fix GenImageGradientSquare and add to textures_image_generation example
* Remove params from GenImageGradientSquare
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.