Rename pipe states so they are more mnemonic

Removed tracing on router option setting

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Add ROUTER socket option to introduce self(send an empty message) to new peers, to allow ROUTER<->ROUTER auto-discovery problem.

Working on Travis builds

- made consistent with options.cpp code
- added trace print for ongoing issue with Travis CI builds

Adding support for Travis CI

stdint.h isn't available on all platforms

Added as_server to options

- we need to switch to PLAIN according to options.mechanism
- we need to catch case when both peers are as-server (or neither is)
- and to use username/password from options, for client

Use socket options to select security mechanism

Added options for PLAIN security

* ZMQ_PLAIN_SERVER, ZMQ_PLAIN_USERNAME, ZMQ_PLAIN_PASSWORD options
* Man page changes to zmq_setsockopt and zmq_getsockopt
* Man pages for ZMQ_NULL, ZMQ_PLAIN, and ZMQ_CURVE
* Test program test_security

Implement ZMTP/3.0 PLAIN mechanism

This implements protocol handshake.
We still need to design and implement 1) API changes so a user
can set username and password, and 2) a mechanism for engine
to authenticate users.

Some changes to building and packaging

Implement ZMTP/3.0 NULL mechanism

zmq_msg_close clarification in man pages