code: @GwtIncompatible("incompatible method")
      public StrBuilder appendln(final String format, final Object... objs) {
          return append(format, objs).appendNewLine();
      }
docs: Calls {@link String#format(String, Object...)} and appends the result.
  
  @param format the format string
  @param objs the objects to use in the format string
  @return {@code this} to enable chaining
  @see String#format(String, Object...)
  @since 3.2