Adds beginnings of doOnEach operator
Adds other overrides for doOnEach
Adds scala adapters for doOnEach operator
Wraps DoOnEach in a SafeObserver

This commit leverages the SafeObserver facility to get the desired
behavior in the face of exceptions.  Specifically, if any of the
operations performed within the doOnEach handler raises an exception,
that exception will propagate through the observable chain.
Merge pull request #479 from nullstyle/add_doOnEach

Adds doOnEach operator