Redactor - Superscript button Is there a possibility to ad a 'superscript' button to redactor?

Edit: I found an explanation here: How can I use &lt;small&gt; &lt;sub&gt; &lt;sub&gt; within a redactor/rich-text field?

But I can't get it to work.

I copy this snippet form: http://imperavi.com/redactor/examples/buttons-sup-and-sub/ to  craft/app/resources/lib/redactor/plugins/subsup.js

if (!RedactorPlugins) var RedactorPlugins = {};

RedactorPlugins.scriptbuttons = function()
{
    return {
        init: function()
        {
            var sup = this.button.add('superscript', 'Superscript');
            var sub = this.button.add('subscript', 'Subscript');

            // make your added buttons as Font Awesome's icon
            this.button.setAwesome('superscript', 'fa-superscript');
            this.button.setAwesome('subscript', 'fa-subscript');

            this.button.addCallback(sup, this.scriptbuttons.formatSup);
            this.button.addCallback(sub, this.scriptbuttons.formatSub);
        },
        formatSup: function()
        {
            this.inline.format('sup');
        },
        formatSub: function()
        {
            this.inline.format('sub');
        }
    };
}; 


Then I call the plugin in a custom.json file like this:

{
    buttons: ['link','bold', 'italic','unorderedlist','orderedlist','image','html'],
    plugins: ['fullscreen', 'subsup'],
    toolbarFixedBox: true
}


But that results in nothing. What do I miss?
I had a similar problem so created a plugin to add some of these extras to Redactor.

Redactor Extras for Craft

https://github.com/elliotlewis/Redactor-Extras
Available plugin are:


Superscript and Subscript
Word count
Alignment
Custom plugin