Added support for replicaSet mongo setup

Add support for replicaSet mongo setups by passing in an array of server parameters in the form of [<hostname>, <port>, <options>] to the options hash key 'mongo-hosts' 

eg.
[
	['db1.domain.com', 27017, { auto_reconnect: true, slave_ok: true }
	['db2.domain.com', 27017, { auto_reconnect: true, slave_ok: true }
	...
]