Add skybox post-processing + general post process improvements

[edunad]

Description

• Add post processing skybox
• Add ability to turn on and off post process plugins
• Improve dithering
• Add drawText background

Closes #39

[github-actions[bot]]

Cpp-Linter Report :warning:

Some files did not pass the configured checks!

clang-format reports: 1 file(s) not formatted

- rawrbox.math/include/rawrbox/math/color.hpp

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