myst-parser 0.8.0

Move to markdown-it-py parser

on Python PyPI

Implemented in #123

This release implements the move from mistletoe to markdown-it-py, as the underlying markdown parser. The reason for this is are discussed in executablebooks/meta#44 (comment) and executablebooks/meta#47, and the PR #123 discusses in more details the update.

Additional changes:

• Update pydata-sphinx-theme requirement
• Improve testing and move to GitHub Actions CI
• Add tests and fixes for reporter warnings and include directive
• Add documentation of sphinx parser options
• Apply doc fixes suggested by @rossbar in #121
• Add warning for non-consecutive headings