Add RELICENSING statement for bl0x.

RELICENSE/bl0x.md

+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Bastian Löher that grants permission to
+relicense its copyrights in the libzmq C++ library (ZeroMQ) under the
+Mozilla Public License v2 (MPLv2) or any other Open Source Initiative
+approved license chosen by the current ZeroMQ BDFL (Benevolent
+Dictator for Life).
+
+A portion of the commits made by the Github handle "bl0x", with
+commit author "Bastian Löher <me@l-dot.de>", are
+copyright of Bastian Löher.  This document hereby grants the libzmq
+project team to relicense libzmq, including all past, present and
+future contributions of the author listed above.
+
+Bastian Löher
+2019/08/01