docs: Fix a few typos

[timgates42]

There are small typos in:

• README.rst
• doc/usage.rst
• pycarddav/init.py
• pycarddav/backend.py
• pycarddav/controllers/sync.py
• pycarddav/model.py

Fixes:

• Should read separated rather than seperated.
• Should read utilities rather than utilies.
• Should read overridden rather than overriden.
• Should read sure rather than shure.
• Should read formatted rather than formated.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md