Fresh version of #93: Add logging of commands, connects and disconnects

This branch [is argued](https://github.com/andymccurdy/redis-py/pull/93#issuecomment-668917) to add logging capabilities costing only 0.2% slowdown.

Please consider merging it and then updating the docs on the usage of the new feature, as I am unsure on how to enable, if different from standard.