* Move project tests to its own directory.
* Install mock test dependency for Python2 only.
* Do not install tox inside tox environment.
* Exclude tests from sdist.
* Use recent pip on Travis-CI.
As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:
> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.
Test Plan: Manually visited all the links I’ve modified.
