Wrap BtMessage objects by std::unique_ptr instead of std::shared_ptr
Code cleanup
Use std::unique_ptr for ExtensionMessage
Use std::unique_ptr for ProgressUpdate instead of raw pointer
Use std::unique_ptr to store DHTMessages instead of std::shared_ptr
Use std::unique_ptr in DHTRegistry
Fix segmentaion fault
Use std::unique_ptr for MessageDigest
Use std::unique_ptr for AsyncResolverMan