UNSUPPORTED made public so that user's can add UNSUPPORTED conversion…

…s to block overly broad inheritance.

src/main/java/com/cedarsoftware/util/convert/Converter.java

@@ -69,7 +69,7 @@
  */
 
 public final class Converter {
-    static final Convert<?> UNSUPPORTED = Converter::unsupported;
+    public static final Convert<?> UNSUPPORTED = Converter::unsupported;
     static final String VALUE = "_v";
 
     private final Map<Map.Entry<Class<?>, Class<?>>, Convert<?>> factory;