Allow parallel builds.

[anntzer]

Return metadata as in http://www.sphinx-doc.org/en/master/extdev/index.html#extension-metadata: there is no reason to prevent parallel builds when using sphinx-jinja.

You may also want to return a version here, I'll let you decide where you want to pull it from (e.g., define __version__ and return it in setup).

[tardyp]

thanks!

[anntzer]

I have another one coming and that's all :)