Gist plugin: ignore trailing slashes and anchors

Supersedes #783

js/plugins.js

@@ -435,11 +435,12 @@ plugins.factory('userPlugins', function() {
 
     // Embed GitHub gists
     var gistPlugin = new UrlPlugin('Gist', function(url) {
-        var regexp = /^https:\/\/gist\.github.com\/[^.?]+/i;
+        // ignore trailing slashes and anchors
+        var regexp = /^(https:\/\/gist\.github.com\/(?:.*?))[\/]?(?:\#.*)?$/i;
         var match = url.match(regexp);
         if (match) {
             // get the URL from the match to trim away pseudo file endings and request parameters
-            url = match[0] + '.json';
+            url = match[1] + '.json';
             // load gist asynchronously -- return a function here
             return function() {
                 var element = this.getElement();