Add support for replica sets and sharded clusters

[jacurtis]

I want to support replica sets and sharded clusters. I wouldn't be hard to configure this as it only requires editing the createUri() method and a few changes to the config file.

[jacurtis]

This could be added by making the 'host' configuration setting into an associative array. The array would include a port and a uri for each one.

Another option would be to just allow them to create the full uri themselves, but maybe thats another issue to create.