Support pandoc-style citations

[cben]

This probably means:

• [ ] a way for user to supplies a bibtex file (global file per user? research Zotero / Mendeley / citeulike etc integration...)
• [ ] autocomplete of citation keys
• [ ] tooltip showing full citation, behave like a clickable link (#9)

[cben]

APIs to integrate with (waa-y into the future):

• [ ] Zotero
• [ ] Doccear doesn't have a documented API but is fully open.
• [ ] Mendeley
• [ ] Some universal way to link a .bib file from another reference manager and keep it up-to-date — e.g. user puts it in Dropbox and shares with mathdown.

Also, search in large open-data indexes like Citeseer and DBLP might be nice.

[cben]

BTW, syntax highlight is currently absent (but is not broken either). Ideal behavior would be similar to footnotes (#40).