New command: ./elefant helper-info admin/util/modal

[jbroadway]

This should render the markdown found in the first block comment at the top of the file, e.g.,

<?php // apps/myapp/handlers/util/helpername.php

/**
 * This helper does x, y, and z.
 *
 * Usage:
 *
 *     {! myapp/util/helpername !}
 */

So that ./elefant helper-info myapp/util/helpername would output:

# myapp/util/helpername

This helper does x, y, and z.

Usage:

    {! myapp/util/helpername !}

These comments could also form the basis of a helper reference section on the website.