Added zmq_msg_send/recv functions

Renamed zmq_getmsgopt to zmq_msg_get

* Added zmq_msg_poke for orthogonality
* Added zmq_msg_more for simplicity
* Fixed up man pages and test program

Cleanups to man pages

Fixed error in documentation build

This reverts commit e646ce43.

- anonymous contributor

This reverts commit 7b7d4042.

Wildcard support in TCP and IPC addresses

provide type safe sockets and contexts

more checks for parameters of API functions

fix warn unused variables

Provide scatter/gather array I/O

We have to use an incomplete type in the interface.
The definition of iovec is only in the implementation.
This appears to following existing practice in 0MQ.
It seems a bit flakey that zmq.h is not included in zmq.cpp,
which is normal practice to ensure the implementation matches
the specified interface. YMMV. I follow 0MQ style.

Also move iovec definition from implementation to interface.
Not clear to me at present if an incomplete type should
be used to avoid gratuitously including <sys/uio.h> in
the interface. The interface can't be used with this include.

Posix style send multiple messages using scatter/gather array.

sys/uio.h contains the XSI vector I/O data structure.

Fix comments to conform to style guide.