code: public AbstractBuilder getClassBuilder(TypeElement typeElement,
              TypeElement prevClass, TypeElement nextClass, ClassTree classTree) {
          return ClassBuilder.getInstance(context, typeElement,
              writerFactory.getClassWriter(typeElement, prevClass, nextClass, classTree));
      }
docs: Return the builder for the class.
  
  @param typeElement the class being documented.
  @param prevClass the previous class that was documented.
  @param nextClass the next class being documented.
  @param classTree the class tree.
  @return the writer for the class.  Return null if this
  writer is not supported by the doclet.