Added a preview template

Ported over from devtools-docs repo.

_preview.js

@@ -0,0 +1,35 @@
+
+(function(){
+
+	var file = document.location.search.replace(/\?/,'');
+	var link = document.createElement('a');
+	var listing = false;
+
+	// get directory listing if no URL provided
+	if (!file){
+		listing = true;
+		file = '/';
+	}
+
+	// let's ajax it in
+	var content = jQuery('<div>').load(file, function(res){
+
+		var self = $(this), ext = file.split(".");
+
+		if(ext[ext.length - 1] == "md")
+		self[0].innerHTML = marked.parse(res);
+		self.prependTo('#gc-content');
+
+		// muck with the content
+		if (!listing) return;
+
+		self.find('a[href]')
+			.filter('a[href$="/"]').closest('li').remove().end().end()
+			.attr('href', function(el, oldattr){
+				link.href = oldattr;
+				return location.pathname + '?' + link.pathname.replace(/\/docs\//,'');
+			});
+
+	});
+
+}());