code: public ClassDoc[] interfaces() {
          ListBuffer<ClassDocImpl> ta = new ListBuffer<>();
          for (Type t : env.types.interfaces(type)) {
              ta.append(env.getClassDoc((ClassSymbol)t.tsym));
          }
          //### Cache ta here?
          return ta.toArray(new ClassDocImpl[ta.length()]);
      }
docs: Return interfaces implemented by this class or interfaces
  extended by this interface.
  
  @return An array of ClassDocImpl representing the interfaces.
  Return an empty array if there are no interfaces.