More javadocs and cleanup
Memebership.shutdown() and enabled() return true is the command caused
an online/offline change.
more javadocs and cleanup.
-Able to obtain the Key of the predecesor
(getPreviousNodeTo(requestedKey)). 
-Able to obtain the Key of a online predecesor
(getPreviousNodeResponsible(requestedKey)).
-Tested using ConsistentHashing.main().

-Added helper methods to MemebershipProtocol to allow testing from
ConsistentHashing.main(). These helper methods are public and should be
private before deploying (for correctness).
Cleanup.
Detected potential Bug in ConsistentHashing.getNodeResponsible(). Needs
to be resolved based on what the expected behaviour is. The bug is
reproducible, using ConsistentHashing.main()
Proposed solution in FIXME tag within method.