Got rid of async connection, async session and async operations.  Add Protocol.executeAsync and implementations for all protocols.
Added AsyncOperation and made most implementations implement it.
Moved protocol package out of operation
Moved message classes into protocol.message
Move classes from org.mongodb.connection.impl to org.mongodb.connection
Moved ChainingServerSelection from connection to session
Renamed ChannelProviderSettings to ConnectionPoolSettings
Collapsed authentication helpers since the async authenticators are gone