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

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

LoadSpriteFontTTF() --> LoadSpriteFontEx()

- Removed raylib_demo (outdated)
- Removed some old examples

Some tweaks on original src files

- Removed rbmf font example
- Reviewed physac examples

Moved to custom example, now raylib only supports simulated VR
rendering.
Oculus code was too device dependant... waiting for OpenXR.

Supports line thickness

According to Man Pages, timespec with std=c99 needs "_POSIX_C_SOURCE 199309L". Due a some kind of bug, "#define _POSIX_C_SOURCE 199309L" doesn't work, so we must use "-D_POSIX_C_SOURCE=199309L" in compiler options.

Also reviewed issue with stdbool when compiling with clang