bring back server.router.render

Took the base code from latest version 6 and applied the version 7 routing.

fixes restify#1684

lib/router.js

@@ -114,6 +114,45 @@ Router.prototype.lookupByName = function lookupByName(name, req, res) {
     return route.chain.run.bind(route.chain);
 };
 
+/**
+ * Takes an object of route params and query params, and 'renders' a URL.
+ *
+ * @public
+ * @function render
+ * @param    {String} routeName - the route name
+ * @param    {Object} params -    an object of route params
+ * @param    {Object} query -     an object of query params
+ * @returns  {String} URL
+ */
+Router.prototype.render = function render(routeName, params, query) {
+    var self = this;
+
+    function pathItem(match, key) {
+        if (params.hasOwnProperty(key) === false) {
+            throw new Error(
+                'Route <' + routeName + '> is missing parameter <' + key + '>'
+            );
+        }
+        return '/' + encodeURIComponent(params[key]);
+    }
+
+    function queryItem(key) {
+        return encodeURIComponent(key) + '=' + encodeURIComponent(query[key]);
+    }
+
+    var route = self._registry.get()[routeName];
+
+    if (!route) {
+        return null;
+    }
+
+    var _path = route.spec.path;
+    var _url = _path.replace(/\/:([A-Za-z0-9_]+)(\([^\\]+?\))?/g, pathItem);
+    var items = Object.keys(query || {}).map(queryItem);
+    var queryString = items.length > 0 ? '?' + items.join('&') : '';
+    return _url + queryString;
+};
+
 /**
  * Adds a route.
  *