docs: Reference Documentation

[gaocegege]

Please help migrate documentation from Processing to Processing.R -- pick any function and add a reference page, example, and test!

Detailed instructions here:

• https://github.com/gaocegege/Processing.R/wiki/How-to-document-Processing.R

ref https://github.com/gaocegege/Processing.R/wiki/Documentation-and-E2E-Test-Generator-Tool

• Shape
• Lights, Camera
• Transform
• Structure
• Environment
• Data
• Control
• Input
• Output
• Image
• Rendering
• Typography
• Math
• Constants