Changed support for constants in repeating groups to use instance ini…

…tialisation rather than static initialisation to address issue #3.

main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -852,7 +852,7 @@ private CharSequence generateConstPropertyMethods(final String propertyName, fin
 
         sb.append(String.format(
             "\n" +
-            indent + "    private static final byte[] %sValue = {%s};\n",
+            indent + "    private final byte[] %sValue = {%s};\n",
             propertyName,
             values
         ));