Add support for UUID version 1 to UUIDFactory

Also improved documentation and minor cleanup.

The UUID1 implementation is standardized and compatible with other implementations, such as [python's uuid.uuid()](https://docs.python.org/2/library/uuid.html#uuid.uuid1). 

@adamvoncorswant @fredrikbackstrom Please have a look.
Nice. I don't think that the time needs to be perfected more than what is already in `DeterministicTimeUUIDFactory`. As long as the second part is random enough, I  think we're good!