Prepare release 2.2.0

Update CHANGELOG.md

Add tests for strictly typed settings (#182)

- Add regression test for #178
- Bump version

Remove commit history notes from changelog (#176)

Fix: Limit django-storages to <1.9 (#168)

In django-storages 1.9 the long deprecated boto storage has finally been removed, see https://github.com/jschneier/django-storages/blob/master/CHANGELOG.rst#19-2020-02-02

switch to pytest and fix #157

- Fix #157: catch pydoc.ErrorDuringImport
- Remove runtests.py and use pytest instead
- Add Python 3.8 to test matrix
- Update copyright note in readme
- Add deprecation warning for using BotoStrategy

#122: implement google cloud support

Co-authored-by: Jeremy Nauta <jeremypnauta@gmail.com>

fix: raise ImproperlyConfigured for all unguessable storages

imlement strategy abstraction

Large rewrite to simplify implementing support for more storage backends.
Introduces a `Strategy` abstraction that can be subclassed to implement support
for different storage backends and needs.

Misc.:

- Remove --ignore-etag option
- Get rid of wrapping quotes in hashes, bump cache key version
- Command tests now run with both boto and boto3

bump version