Problem: Incorrect formatting of documentation in zmq_udp.txt

[nevalsar]

Solution: Replace incorrect underline pattern in zmq_udp.txt that makes part of the text show up as pre-formatted code block with regular underline pattern.

http://api.zeromq.org/master:zmq-udp

[bluca]

Please add a relicense statement https://github.com/zeromq/libzmq/tree/master/RELICENSE