Syntax highlighting for ngDocs

Adds syntax highlighting for the angularjs-specific flavor of jsDocs.

Specifically:

With params:  ngdoc, methodOf, propertyOf, eventOf, link, restrict, eventType, scope, priority.
No params: animations

https://github.com/angular/angular.js/wiki/Writing-AngularJS-Documentation#wiki-the-ngdoc-directive
https://github.com/m7r/grunt-ngdocs