Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Multicast loopback is not a real multicast, rather a kernel-space
simulation. Moreover, it tends to be rather unreliable and lossy.
Removing the option will force users to use transports better
suited for the job, such as inproc or ipc.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

- Clarify ZMQ_LINGER, zmq_close (), zmq_term () relationship
- New socket options
- Clarify thread safety of sockets and migration between threads
- Other minor and spelling fixes
Signed-off-by: Martin Lucina <mato@kotelna.sk>

This reverts commit 77a3c36f.

This reverts commit 13f3481e.

Conflicts:

	doc/zmq_device.txt
	doc/zmq_tcp.txt

- fixed unwrapped text in new man pages
- fixed over-long lines in older pages, where possible
- removed reference to old standalong devices from index page
- added refernce to new zmq_device[3] documented from index page
- some minor spelling corrections

* Added documentation for zmq_deviced, which we're developing
* Created consistent page footer in documentation template
* Page footer notes doc authors and copyright statement