* Extend LiveMarkdown format to support Elixir snippets in Markdown cells
* Highlight Markdown code blocks using Monaco editor API
* Use livebook metadata for forcing markdown as well
* Initial file import/export
* Add renderer tests
* Refactor renderer
* Depend only on EarmarkParser
* Add test for export
* Add import tests
* Improve import
* Document the ExMd file format
* Rename ExMd to ExMarkdown
* Rename ExMarkdown to LiveMarkdown
* Build iodata when exporting a notebook
* Persist metadata as a single JSON object
* Move Markdown to LiveMarkdown.MarkdownHelpers
* Make LiveMarkdown private
* Always move primary heading to the top during import
* Hint the user not to use heading 1 and 2
* Return a list of messages from the import function
* Update headings warning
* Add import and export test for non-elixir snippets
* Merge markdown renderer into MarkdownHelpers
* Add import messages on AST rewrites
