Support the use of files paths as well as sha

I have updated the code so a user can specify a github content path and ref. For example:

```HTML
<html>
<head>
<script src="http://code.jquery.com/jquery-1.9.0.min.js" type="text/javascript"></script>
<script type="text/javascript" src="git.js" >
</script>

</head>
<body>
<pre class="github cs" sha="02734cd5b1cc857b4a43760cd958d6a07a42307a">

</pre>

<pre class="github cs" file="docs/concepts/example-fluent-1.cs" ref="gh-pages">

</pre>


<script type="text/javascript">
(function($) {
    $(function () {

        $("pre.github").each(function () {

            var $pre = $(this);
            $pre.addClass("prettyprint");
            
            var sha = $pre.attr("sha");
            var path = $pre.attr("file");
console.log(path);
            var ref = $pre.attr("ref");
            var commit = new GitHubCommit({
                username: "mikeedwards83",
                reponame: "Glass.Mapper",
                fileSHA: sha,
		filePath: path,
                ref: ref


            });

            commit.fetch(function(content) {
                $pre.html(content);
                prettyPrint();
            });
        });

    });
})(jQuery);
</script>
</body>
</html>
```