Add more official plugins

[chrisjsewell]

• [x] https://github.com/markdown-it/markdown-it-container: could be used for https://github.com/executablebooks/MyST-Parser/issues/154
• [x] https://github.com/markdown-it/markdown-it-deflist: https://github.com/executablebooks/MyST-Parser/issues/153
• [ ] https://github.com/markdown-it/markdown-it-abbr: could be used for substitutions https://github.com/executablebooks/MyST-Parser/issues/172?
• [ ] https://github.com/markdown-it/markdown-it-sub: e.g. H~2~0
• [ ] https://github.com/markdown-it/markdown-it-sup: e.g. 29^th^

(and integrate with myst-parser) (also amsmath is still to be integrated, see https://github.com/executablebooks/MyST-NB/issues/126#issuecomment-622935821)

[jace]

@miteshashar ported abbr, sub, sup and other plugins for our app that uses Markdown-It-Py. Code here: https://github.com/hasgeek/funnel/tree/main/funnel/utils/markdown/mdit_plugins. We worked independently as we had a timeline to finish in, but we'll happy to contribute them here.

[miteshashar]

I will be happy to be involved, as necessary.

[chrisjsewell]

That would be great thanks

[miteshashar]

@chrisjsewell I saw your response now – a little too long. I can work on this over the coming few weeks.