[Feature Request] Add markdown extensions support

[LeonardoIz]

Would it be possible to add support for MarkDown extensions?
It would be very useful to be able to use some markdown extensions such as KaTeX, SmartyPaints, Mermaid, etc...

[dullage]

Also similar to #61 and #143.

[LeonardoIz]

Will they be added?

[dullage]

Will they be added?

There currently no plans to add them but it may be something I look at in the future.