Add re-license grant file

Signed-off-by: Christopher Hall <hsw@ms2.hinet.net>

RELICENSE/hsw.md

+# Permission to Relicense under MPLv2 or any other OSI approved license chosen by the current ZeroMQ BDFL
+
+This is a statement by Christopher Hall 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 "hxw", with commit
+author "Christopher Hall <hsw@ms2.hinet.net>", are copyright of
+Christopher Hall.  This document hereby grants the libzmq project team
+to relicense libzmq, including all past, present and future
+contributions of the author listed above.
+
+Christopher Hall
+2019/08/07