* 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

- tests that system can provide at least 1,000 sockets
- we could expand on this but this covers the main case of OS/X
  having a too-low default limit of 256 handles per process