Add relicense permission

RELICENSE/rcxdude.md

+# Permission to Relicense under MPLv2
+
+This is a statement by Douglas Young
+that grants permission to relicense its copyrights in the libzmq C++
+library (ZeroMQ) under the Mozilla Public License v2 (MPLv2).
+
+A portion of the commits made by the Github handle "rcxdude", with
+commit author "Douglas Young <rcxdude@gmail.com>", are copyright of Douglas Young .
+This document hereby grants the libzmq project team to relicense libzmq, 
+including all past, present and future contributions of the author listed above.
+
+Douglas Young 
+2019/08/31