WIP: Markdown formatter

[eksperimental]

Original implementation as discussed in https://github.com/elixir-lang/ex_doc/issues/1962

The generated docs can be seen in this repo: https://github.com/eksperimental/ex_doc_markdown_formatter_docs

This is a WIP. There are many details to fix such as some characters that need to be properly escaped/unescaped.

I would like to get some feedback before moving forward.

My approach was to keep things simple and add things if they are needed.

One challenge was to rewrite the headings levels within docs, since that would break the hierarchical structure of the document.

Screenshots

API REFERENCE

KERNEL

KERNEL