Clarify license status

This copies copyright notice from README to
COPYING as is standard for many projects.

Note: this is not a relicense in any sense, just
moving test around

COPYING

+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose and without fee is
+hereby granted, provided that the above copyright notice appear in all copies.
+Authors make no representations about the suitability of this software for
+any purpose.  It is provided "as is" without expressed or implied warranty.
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