Support of citation reference

[sebhahn]

For example:

org Here is a citation reference \cite{CIT2002}.

rst Here is a citation reference: [CIT2002]_.

.. [CIT2002] This is the citation. It's just like a footnote, except the label is textual.

or should this be part of ox-bibtex? http://orgmode.org/w/?p=org-mode.git;a=blob_plain;f=contrib/lisp/ox-bibtex.el;hb=HEAD