* updated javadoc.
* minor updates here-&-there.
* -ZAbstractTwoWaySocketTest -- it was crap.
* updated all tests which depended on ZAbstractTwoWaySocketTest.
* updated code in ZWorker: created new dependency -- PingStrategy.
* update on ZDispatcher: don't forward PING on frontend.
* minor update.
* small update in test code.
* update to exception-handling.
* +InTheChain interface -- tiny abstraction around "chain-of-responsibility" concept.
* update towards RETRY support.
* -ZMessageSession -- redudant abstraction.
* -RETRY stuff -- no more need to retry ;)
* +ZDispatcherLRU -- finally ...
* moved "edge" package into "io".
* minor updates in the tests.
* refactored significantly code inside ZAbstractMessenger and its subclasses -- looks great now.