Major update (2021/7/5)

Changes since 0.2.0

1. Implement the whole media statistics API
2. Room.lists will now return dict item individually instead of returning the whole dict
3. Return next_token in Management.event_reports
4. Return a dict with user id as key and the event id as value in Management.announce_all
5. Return bool instead of a list in Media.delete_local_media
6. More docstrings
7. Refactored some return line
8. Removed SynapseAPIError

Bug fixed

1. User.lists return one more value now, hence Management.announce_all is broken
2. Fix some broken docstring contents