Create ReadTheDocs page

1. Describe the enhancement you are requesting. Enhancements include:
If lua fibers is to be made open source (and just for our own sake) we should invest the time to make a readthedocs style API documentation which gives a thorough tour of everything needed to use lua fibers.

This is a must-have for open source and a should-have for internal use

The issue names no files, tests, or documentation entry point. Begin by inventorying the public Lua fibers API and existing repository documentation, then define the ReadTheDocs structure and coverage needed for a thorough user tour; done means the documented API and usage path are complete.

Written by the indexing model from the issue text.