[Feature] Improve documentation

[brenocq]

Feature description
@epezent feedback in #24

• Document PlotX functions
• Consider putting the MIT license in your headers

Functions are not well documented in the v0.2 release as pointed out in #24, this should be fixed ASAP to help other developers get familiar with the codebase.

The MIT license should also be added to the header of all files.

Tasks

• Add MIT header to files
• Document public/internal APIs
• Demo SetupAxisFormat
• Demo SetupLegend
• Demo PixelsToPlotRay/PixelsToPlotPlane
• Demo Offset/Stride
• Demo GetPlotRectPos/GetPlotRectSize

[brenocq]

It's about time I work on this... kkkkkk