LaTeX in documentation

[leotrs]

• Add sphinx to requirements.txt. Otherwise make html inside docs complains.
• The docs are very complete but lack a bit in formatting. Using LaTeX for some of the rendering shouldn't be too difficult within sphinx. These changes could go well with the proposed style rewrite.

[aestrivex]

I will get to it at some point. PRs welcome.

[leotrs]

I would add sphinx to the requirements but sphinx 1.4.5 outputs different files on my local repo. I would need to know which sphinx version is currently being used.

I will try to update the docs with some formatting as I go along.