Add relicense grant (#3624)

* Add relicense grant
Signed-off-by: Dhammika Pathirana <dhammika@gmail.com>

RELICENSE/dhammika.md

+# Permission to Relicense under MPLv2
+
+This is a statement by Dhammika Pathirana
+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 "dhammika", with
+commit author "Dhammika Pathirana <dhammika@gmail.com>", are copyright of Dhammika Pathirana .
+This document hereby grants the libzmq project team to relicense libzmq, 
+including all past, present and future contributions of the author listed above.
+
+Dhammika Pathirana
+2019/08/12