textproc/py-sphinxcontrib-bibtex: Add py-sphinxcontrib-bibtex 2.3.0

The bibtex extension allows BibTeX citations to be inserted into documentation
generated by Sphinx, via a bibliography directive, along with :cite:p: and
:cite:t: roles. These work similarly to LaTeX's thebibliography environment and
the \citet and \citep commands.

WWW: https://github.com/mcmtroffaes/sphinxcontrib-bibtex