Extracted Send and SendMore overloads as extension methods for IOutgoingSocket
Created IReceivingSocket interface as a declaration of socket able to receive messages, and extracted Receive/ReceiveString overloads as extension methods to IReceivingSocket interface
Updated ReceiveAll/ReceiveMessages extension methods to extend IReceivingSocket instead of NetMQSocket
Removed excessive method overloads in favor of optional parameters
Moved ReceiveMessage methods to extension methods class
Merge pull request #68 from almazik/feature/reduce_overloads

Reduced the number of overloads defined on NetMQSocket class