Replace lxml with HTMLParser in citation2latex
Update tests
Crop if no endtag is given
Added 18 more citation tests

Thanks @jakobgager for the tests-
http://nbviewer.ipython.org/gist/jakobgager/6859103
Removed a couple blank lines.
Replace <> with != in citation filter (invalid Py3 syntax)
Import HTMLParser from html.parser for Python 3.x
Merge pull request #5025 from jdfreder/jakob-html

citation2latex filter (using HTMLParser)