Add the ZMQAuth class

The ZMQAuth class wraps the CZMQ zauth API.

Instances of the ZMQAuth class can:

* install a ZAP handler for a ZMQContext
* whitelist/blacklist IP addresses
* use plain or curve authentication for one or more domains
Add examples for the ZMQCert and ZMQAuth classes

grasslands.php, strawhouse.php, woodhouse.php, stonehouse.php, and
ironhouse.php are faithful translations of Pieter Hintjens' examples of
the same names, which he originally published as part of his blog post
Using ZeroMQ Security (part 2)[0].

[0] http://hintjens.com/blog:49
Build ØMQ 4.0.1 with and without CZMQ 2.2.0