a [Marked.js](https://marked.js.org) custom extension for [Misskey-flavored Markdown](https://github.com/misskey-dev/mfm.js/blob/develop/docs/syntax.md).
this is a reimplementation of [the original MFM parser](https://github.com/misskey-dev/mfm.js/blob/develop/docs/syntax.md), which was written from the ground up using PEG.js instead of as an extension of CommonMark, and therefore was not up to spec.