LIC: restore LICENSE_PAINT

The png writing code is derived from
https://www.object-craft.com.au/projects/paint/

The original code came in via 6cc5c32
The license was added in 29dfcd2
The license was removed in e3a5f1d

The derived code is currently in `src/_png.cpp`

Author: tacaswell

LICENSE/LICENSE_PAINT

@@ -0,0 +1,20 @@
+Copyright 2000 by Object Craft P/L, Melbourne, Australia.
+
+                        All Rights Reserved
+
+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 and that
+both that copyright notice and this permission notice appear in
+supporting documentation, and that the name of Object Craft
+is not be used in advertising or publicity pertaining to
+distribution of the software without specific, written prior
+permission.
+
+OBJECT CRAFT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+EVENT SHALL OBJECT CRAFT BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
+USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.