add Arm to the copyright file
Several math functions are now from the ARM optimized-routines repo
licensed under standard MIT terms and copyrighted by Arm Limited,
so mention this in the COPYRIGHT too.
diff --git a/COPYRIGHT b/COPYRIGHT
index 2525ffb..67802d1 100644
--- a/COPYRIGHT
+++ b/COPYRIGHT
@@ -122,7 +122,8 @@
Copyright © 2003-2011 David Schultz or
Copyright © 2003-2009 Steven G. Kargl or
Copyright © 2003-2009 Bruce D. Evans or
-Copyright © 2008 Stephen L. Moshier
+Copyright © 2008 Stephen L. Moshier or
+Copyright © 2017-2018 Arm Limited
and labelled as such in comments in the individual source files. All
have been licensed under extremely permissive terms.