Grant by kreuzberger

Received via Github comment:
https://github.com/zeromq/libzmq/pull/1374#issuecomment-527100078

RELICENSE/kreuzberger.md

+# Permission to Relicense under MPLv2
+
+This is a statement by Joerg Kreuzberger
+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 "kreuzberger", with
+commit author "Joerg Kreuzberger", are copyright of Joerg Kreuzberger .
+This document hereby grants the libzmq project team to relicense libzmq,
+including all past, present and future contributions of the author listed above.
+
+Joerg Kreuzberger
+2019/09/02