* Removed redundant Z85 code and include files from project
* Simplified use of headers in test cases (now they all just use testutil.hpp)
* Export zmq_z85_encode() and zmq_z85_decode() in API
* Added man pages for these two functions

* Removed or truncated sleeps so the tests run faster
* Removed dependencies on zmq_utils
* Rewrote a few tests that were confusing
* Minor code cleanups

in order to avoid logical collisions with pre-existing notions of context destruction in bindings (czmq, pyzmq).

- fixes LIBZMQ-476 and LIBZMQ-475