Renamed MongoServerBinding to Cluster, and sub-classes accordingly.  Renamed all variables from binding to cluster and methods from getBinding to getCluster
Renamed MongoServer to Server
Renamed MongoSyncConnection to Connection, renamed MongoAsyncConnection to AsyncConnection, renamed MongoConnection to BaseConnection.  Sub-classed renamed accordingly.
Moved Session to the right package
Added AsyncSession and implementations, refactored AsyncOperation subclasses to use it instead of Cluster.