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

* Replaced GenImageGradientH and GenImageGradientV with GenImageLinearGradient

* renamed GenImageLinearGradient to GenImageGradientLinear

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.

* Added support for additional mouse buttons

* Renamed mouse button enum

Co-authored-by: Lambert Wang <lambert.ww@gmail.com>

- Some examples tweaks
- Reviewed ImageFormat()
- Use float for text fontSize

Added support for noise image offset

Namely:
- GenImageHorizontalV
- GenImageHorizontalH
- GenImageChecked
- GenImageWhiteNoise
- GenImageCellular

The gradient implementation may be a bit naive, for example it doesn't do any gamma correction.