v0.7.0-rc1

This Release Candidate brings a number of exciting changes, with the switch to EasyMDE as the main one.

Do run pip install wagtail-markdown==0.7.0-rc1 and test it in your builds! 🚀

Changelog:

• Switched to using EasyMDE #76 - Thank you @StefanUlbrich
• Added support for extensions config via WAGTAILMARKDOWN_EXTENSIONS_CONFIG #77 - Thank you @StefanUlbrich, as well as @nrempel for #75
• Removed deprecations
• Added pre-commit support.
  When contributing, run pre-commit install in the wagtail-markdown directory, if you haven't already
• Switched to SemVer and GitHub Actions
• Updated bleach minimum version to 3.3.0. See GHSA-vv2x-vrpj-qqpq