We're going to use the `net4people_url` BibTeX key to link to a paper's
net4people discussion. BibTeX parsers don't know about this key and
should therefore ignore it.
bibliogra.py requires Python 2, which is a pain to deal with. This
commit adds a Go tool that compiles CensorBib from BibTeX to HTML. The
tool does the bare minimum and is quite strict in the BibTeX format it
expects.