* updated TODO.
* created unit tests on basic socket combinations like: REQ/REP, DEALER/REP, REQ/ROUTER, DEALER/ROUTER, PUB/SUB and PUSH/PULL.
* renamed everywhere (except comments) peer_identity --> identity.
* did a lot of renaming_work.
* normalized package structure -- made it simpler.
* +good tests on DEALER/REP.
* +ZRouter basic unit_test: REQ <--> ROUTER-DEALER <--> REP.
* +javadoc.
* +few new tests.
* updated TODO.
* +abstraction around ZChannel and concrete zmq_socket ==> ZClientTemplate and corresponding ZClientFactory.
* refactored tests, since with "client_api" test code became looking much cleaner.
* updated TODO.
* fixed BUG in ZWorkerPool.