Merge pull request #293 from hintjens/master

Fixed response to file handle exhaustion
Add an "add" function for zpoller.

Added a function to add a reader after the initial poller has been
created. I'm not sure how correct this patch is but it passes the self
test. I figured that because both the use case and the patch still
conforms to the zpoller description that it'll be okay.

Also can I get discussion on the documentation and function name for
this?

Use Case:
Creating sockets in a loop and adding them to a poller after it's been
created.

Limitations:
  * Appends a reader so it'll have the lowest priority.
  * There's no corresponding remove function.

Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>
Merge pull request #298 from shancat/feature/poller_add

Add an "add" function for zpoller.
Docs seem to be out of date so update them.

I did this by running this:
```
./autogen.sh
./configure
cd doc
make
```

Signed-off-by: Shannen Saez <shannenlaptop@gmail.com>
Merge pull request #300 from shancat/feature/doc_update

Docs seem to be out of date so update them.
Fixed to make work with ZMQ v3.2
Extending Travis CI build to ZMQ 3.2
Extending Travis CI build to ZMQ 3.2
Disabled zmonitor for libzmq v3.2

- current code assumes libzmq v4.x
- whole class and interface is null now when built on libzmq < v4
Fixed zpoller for ZMQ v2
Added zcert_meta_keys method

This gives the caller a list of all the keys in the metadata.
Updated year
Fixed zauth selftest

- was sometimes failing particularly on Travis CI
- had some grunky code due to ZeroMQ's weakness in changing security on
  existing sockets
- now just recreates sockets every time, which is more robust and works
  as normal applications would work
Added pack/unpack methods

- to support FILEMQ protocol and others using same cheap/nasty codecs
- packs hash table into zframe
- designed for protocol headers, max. 255 values, key+value max 255 chars
Minor style changes
Allow project to survive without README