Add sphinx to Travis installs

[garrettwrong]

Closes #359 , hopefully restoring the automatic doc generation Vineet setup for us a while back.

[janden]

Wouldn't it make more sense to add this to install_requires? (That's where sphinxcontrib-bibtex and co live.)

[garrettwrong]

I am not actually installing aspire on Travis directly anymore (that is actually the root of the issue). pip install aspire will already install sphinx... no need to add to setup.py, though I guess we could call it out.

Instead of the direct install, the CI tests is done inside tox virtual envs.

Im not 100% on this change resolving, maybe 90%, ... but I didn't really design this setup, just trying to work with it... As it is written it is sort of hard to iteratively test it.

[garrettwrong]

Now that Travis is defunct (we're out of time for the month on day 0), this isn't going to kick off anyway.

I'd still put this change in... and I can roll out the 0.6.2 package, then try to manually push the latest docs.

[janden]

That's funny…

Yeah let's do that, then.