Add asynchronous versions of operations

[christav]

Java supports async i/o, we should add true async versions of our operations instead of forcing customers into manual thread management.

[gcheng]

this is a good idea, Jersey supports AsyncWebResources which can be used to implement Async response processing.

[gcheng]

http://docs.oracle.com/javaee/6/tutorial/doc/gkkqg.html

http://nurkiewicz.blogspot.com/2013/02/javautilconcurrentfuture-basics.html