When I was fixing urls the other day, I noticed that sphinx hadn't added
https but there was an open ticket: https://github.com/sphinx-doc/sphinx/issues/5522

Now that that is resolved, I'm updating it here.

`six.moves` is a dynamically-created namespace that doesn't actually
exist and therefore `pylint` can't statically analyze it.

By default, `pylint` is smart enough to realize that and ignore the
import errors.

However, because we vendor it, the location changes to
`kafka.vendor.six.moves` so `pylint` doesn't realize it should be
ignored.

So this explicitly ignores it.

`pylint` documentation of this feature:
http://pylint.pycqa.org/en/1.9/technical_reference/features.html?highlight=ignored-modules#id34

More background:
* https://github.com/PyCQA/pylint/issues/1640
* https://github.com/PyCQA/pylint/issues/223

This is needed for https://github.com/dpkp/kafka-python/pull/1540

While the usage there is trivial and could probably be worked around, I'd
rather vendor it so that future code can use enums... since `enum` is
already available in the python 3 stdlib, this will be easy enough to
eventually stop vendoring whenever we finally drop python 2 support.

Use vendored `six`, and also `six.moves.range` rather than `xrange`

Snappy URL was outdated. Similarly, many of these sites now support
https.

Bump `six` to `1.11.0`. Most changes do not affect us, but it's good to
stay up to date. Also, we will likely start vendoring `enum34` in which
case https://github.com/benjaminp/six/pull/178 is needed.

Note that this preserves the `kafka-python` customization from https://github.com/dpkp/kafka-python/pull/979
which has been submitted upstream as https://github.com/benjaminp/six/pull/176 but not yet merged.