code: protected AbstractConfiguration addMixInAnnotations( Class<?> target, Class<?> mixinSource ) {
          mapMixInAnnotations.put( target, mixinSource );
          return this;
      }
docs: Method to use for adding mix-in annotations to use for augmenting
  specified class or interface. All annotations from
  <code>mixinSource</code> are taken to override annotations
  that <code>target</code> (or its supertypes) has.
  
  @param target Class (or interface) whose annotations to effectively override
  @param mixinSource Class (or interface) whose annotations are to
  be "added" to target's annotations, overriding as necessary
  @return a {@link com.github.nmorel.gwtjackson.client.AbstractConfiguration} object.