Tying down Gemfile dependencies, which comes with coffee-script upgrade
Updated coffee-script gem no longer provides `coffee` binary. `compile` task revised to use CoffeeScript.compile.
Various changes lifted from a project override to the fork:

 * Introduced data-intro-position to avoid clashes with other libraries' usage of the data attribute
 * When $.fn.chardinJs is called, it also adds the class "chardinated" to that element
 * Used the chardinated wrapper class to define a general style for dealing with existing fixed-position elements:
    * Without this change, fixed items remain un sync'ed with the overlay help items
    * Applies to items with class name including "-fixed", as in the Bootstrap case "navbar-fixed-top"
 * Used that same class distinction to temporarily adjust those fixed wrappers' z-index
    * If the item had a custom z-index and was fixed, it would not get displayed above the overlay even if it was intended to
    * These things get reset to their originals simply by the remval of the "chardinated" class on the "chardinJs:stop" event
 * Chardin help text text-aligned as befits the requested position of the help text:
    * Default => text-align: center
    * data-position: left => text-align: right
    * data-position: right => text-align: left
 * Recompiled assets with upgraded CoffeeScript 2.2.0, which most notably removes the intial byline