Merge pull request #1109 from hintjens/master

Set EINVAL on invalid tcp:// endpoint in zmq_connect
Merge pull request #1110 from hintjens/master

Reverted removal of [ ] support
Merge pull request #1111 from hintjens/master

Problem: zmq_msg_gets did not set errno on unknown properties
Problem: two header files for a single library

Users who need e.g. zmq_curve_keypair() have to remember to include
zmq_utils.h, which is counter-intuitive. The whole library should be
represented by a single include file.

Solution: merge all contents of zmq_utils.h into zmq.h, and deprecate
zmq_utils.h. Existing apps can continue unchanged. New apps can ignore
zmq_utils.h completely.