Make estension version available from sphinx

[callegar]

This is meant to allow other extensions to depend on a specific version of numpydoc or to base their behavior on the version of numpydoc that is available.

[rgommers]

This is pretty straightforward, so can review/merge before the 0.7.0 release. @callegar sorry no one got around to reviewing it earlier. Can you rebase?

[jschueller]

there's already a version string in init.py

[callegar]

Yes, it has been added 6 months ago.

Now, a lot of time has passed, and I do not remember 100% of the matter, but if I do remember properly, it does not seem to solve the whole of the problem.

• It cannot be easily read from setup.py, so this information needs to be duplicated there and duplication is errorprone
• It is hardwired in __init__, and thus harder to automatically generate based on VCS tags, if in the future there is the intention to do so (e.g. by python-versioneer)
• It is still not exported in the package metadata as sphinx expects.

[rgommers]

Still needs a rebase. _version.py is good to keep, the regular expression version parsing needs to go (current setup.py has a much more readable way of parsing the version string).

Looks good to merge once that's done.

[rgommers]

Sorry, just see that I missed gh-94.