Add "Export as PDF" functionality

[djungowski]

It would be nice to have the possibility to export a document to PDF, so that others that don't have a Markdown Editor can read the document too

[brhx]

This is an interesting idea, and as @dvcrn would say: "pull requests are always welcome"!

On a more practical note, exporting .md files to a PDF using the GitHub markdown formatting is a common feature among lots of markdown editors. I imagine there are a wealth of libraries out there that could take care of the heavy lifting that shouldn't be too hard to implement.

[dvcrn]

I think for this we could use something like jsPDF to directly export the HTML tree as PDF. I didn't test it yet but if someone wants to tree, please go for it!

[vossilius]

+1