Make a unix_socket_path configurable
Add RedisClientConfiguration object
Pep8
Readd defaults
Describe how to use the socket_path
Test for None not if key is set.

Key is set in DEFAULT config
Configure Client with return statement

The RedisClient configuration is a specialized dict, which
configures and returns itself, if called with the right options.
PEP-8
Default to URL configuration

If socket configuration is not explicitly given, the default
URL will be used (as implied by config). Also fail better, if
somehow neither is provided.
Merge pull request #2 from rdrongow/master

Support unix socket configuration.