code: String signature(ExecutableElement e) {
          StringBuilder sb = new StringBuilder("(");
          String sep = "";
          for (VariableElement p: e.getParameters()) {
              sb.append(sep);
              sb.append(types.erasure(p.asType()).toString());
              sep = ",";
          }
          sb.append(")");
          return sb.toString();
      }
docs: c.f. MethodDoc.signature