Add reST conventions.

There are a lot of files, but most were just updated to match the conventions. You only need look at:

- `.editorconfig` (first file)
- The *reStructuredText Conventions* section of `manual/contributing/guidelines.rst` ([click here](https://github.com/seanfisk/mastering-eos/compare/sean/rst-guidelines?expand=1#diff-a7a537ae0c2706cc8ff4860e7c7b6dfdR24))