* Refactor the documentation build process
Significant improvements:
* Allow easy isolated local builds via a dedicated Tox environment
* Configure Sphinx to use consistent packages and theme across local, CI,
and ReadTheDocs builds; local builds now look the same as the published
RTD pages
* Explicitly add a ReadTheDocs configuration as code, per their documented
best practices
* Remove lots of dead code and simplify the Sphinx configuration file
* Build docs in a dedicated CI step and enable stricter warning checking
* Fix docutils related build error.
* Relax Sphinx version.
* Invalidate RTD build cache.
* No need to combine coverage reporting I think.
* Add combining again.
Co-authored-by: Jannis Leidel <jannis@leidel.info>
* Drop obsolete versions of Django from Travis tests
Django 1.8 reached EOL in April 2018.
Django 1.10 reached EOL in December 2017.
* Add support for testing Django 2.0 and 2.1 on Python 3.7
* Drop obsolete test (requires Django < 1.10)
Hopefully this saves time for new users of django-configuration (like myself), who "just needed" to lazily evaluate a string inside a dictionary.
This doubles as an example for `RAVEN_CONFIG` which was the whole reason I was here in the first place... The actual problem I faced was that a setting remains of type `values.Value` when nested inside a dictionary. Which results in a weird issues like this:
```
2018-02-24T20:59:26.125208+00:00 app[web.1]: Traceback (most recent call last):
2018-02-24T20:59:26.125364+00:00 app[web.1]: self.client.http_context(self.get_http_context(environ))
2018-02-24T20:59:26.125215+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/middleware.py", line 98, in __call__
2018-02-24T20:59:26.125368+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/contrib/django/models.py", line 54, in <lambda>
2018-02-24T20:59:26.125482+00:00 app[web.1]: __getattr__ = lambda x, o: getattr(get_client(), o)
2018-02-24T20:59:26.125486+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/contrib/django/models.py", line 134, in get_client
2018-02-24T20:59:26.125613+00:00 app[web.1]: instance = Client(**options)
2018-02-24T20:59:26.125618+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/contrib/django/client.py", line 147, in __init__
2018-02-24T20:59:26.125769+00:00 app[web.1]: Client.__init__(self, *args, **kwargs)
2018-02-24T20:59:26.125771+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/base.py", line 171, in __init__
2018-02-24T20:59:26.125927+00:00 app[web.1]: self.set_dsn(dsn, transport)
2018-02-24T20:59:26.125929+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/raven/base.py", line 251, in set_dsn
2018-02-24T20:59:26.126063+00:00 app[web.1]: if dsn not in self._transport_cache:
2018-02-24T20:59:26.126076+00:00 app[web.1]: TypeError: unhashable type: 'Value'
```
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.
