Parsing of connection string URI

Adds support for mongo's connection string uri as described in http://docs.mongodb.org/manual/reference/connection-string/.
(based on https://github.com/mongodb/mongo-java-driver/blob/master/src/main/com/mongodb/MongoClientURI.java)

Additionally authenticates the user on connect if credentials were provided (MONGODB-CR).

Pretty much ignores everything else. Throws 'Not Implemented' exception if multiple hosts are specified.