Log Message:
py-ciso8601: updated to 2.2.0

Version 2.2.0

* Added Python 3.9 support
* Switched to using a C implementation of `timezone` objects.
    * Much faster parse times for timestamps with timezone information
        * ~2.5x faster on Python 2.7, ~10% faster on Python 3.9
    * Thanks to [`pendulum`](https://github.com/sdispater/pendulum) and \ 
@sdispater for the code.
    * Python 2.7 users no longer need to install `pytz` dependency :smiley:
* Added caching of tzinfo objects
  * Parsing is ~1.1x faster for subsequent timestamps that have the same time \ 
zone offset.
  * Caching can be disabled at compile time by setting the \ 
`CISO8601_CACHING_ENABLED=0` environment variable
* Fixed a memory leak in the case where an invalid timestamp had a non-UTC \ 
timezone and extra characters