Jnats should use non-blocking NIO2 Sockets instead of legacy blocking IO.

[jameshilliard]

Currently it appears Jnats is using legacy blocking socket streams for the SocketDataPort implementation, this should probably be migrated to use a non-blocking NIO2 AsynchronousSocketChannel for improved performance/latency along with thread safety. I'll probably try and do this myself once #346 is merged.

nats.java/src/main/java/io/nats/client/impl/SocketDataPort.java

Lines 37 to 41 in 031b245

	private Socket socket;
	private SSLSocket sslSocket;
	private InputStream in;
	private OutputStream out;

Is there any reason that Jnats has avoided using NIO2 sockets that I should be aware of? From my initial reading of the code converting to NIO2 sockets should be fairly straight forward as Jnats seems to use the NIO based ByteBuffer's already for messages which is the same buffer format NIO2 based sockets expect for reading/writing.

[brimworks]

Track this need here: #317

Basically, we all want an async client, so let's track that need in the above issue.

Thanks!