REL: v0.11

This is the first Cycler feature release in some years. New features
include:

* Added `Cycler.by_key`, which produces values by key (matplotlib#26)
* Added `Cycler.__contains__`, which adds support for `in` checks (matplotlib#34)
* Wheels now includes the LICENSE file (matplotlib#48)
* The sdist now includes the LICENSE (matplotlib#58) and tests (matplotlib#32)
* Cycler no longer supports Python 2. Supported versions of Python are
  3.6 and above.