* Reader#readAllLines()}. The two may have different performance characteristics for different
   * {@link Reader} classes and Java versions, but both methods read the entire input into memory
   * immediately, so we discourage use of both when memory usage is a concern.
   *
   * @param r the object to read from
   * @return a mutable {@link List} containing all the lines
   * @throws IOException if an I/O error occurs
   */