External plugins guidance and ecosystem

[nixjdm]

Mistune users are able to write there own plugins, and when they do this locally, it is easy enough for them to import and use there plugin code, so it's available when they use Mistune. Is there a preferred way or best practice for how users should publish their plugin? What is the best way one could find community-made plugins? If there are such things, I propose adding them to the docs.

Taking some inspiration from Lektor, projects could be published to pypi with a mistune- prefix so they are discoverable via pypi's search bar, or you could maintain a docs page linking to them. Perhaps PyPA would allow a new trove classifier to list Mistune as a framework, as well (makes sense to me).

I thought of this coming from the idea that Lektor could more easily pull in arbitrary Mistune plugins. lektor/lektor#1076

[lepture]

I've added a community file for mistune v3 plugins: https://github.com/lepture/mistune/blob/v3/docs/community.rst

Developers can send PRs to add their plugins here.