New plugin to get a 'Random' post

I created a new plugin to get a 'Random' post when hitting /random/ url.
Got it! Anyway, I'm not sure that this is useful for me. This is a chunk of that file generated by Nikola:

```
...
u'zeitgeist': [4,
  u'/categories/zeitgeist/',
  {u'posts': [{u'date': u'03/16/2014',
     u'isodate': u'2014-03-16T22:57:40-03:00',
     u'title': u'Z-Day',
     u'url': u'/posts/nikola/z-day.html'},
    {u'date': u'09/17/2013',
     u'isodate': u'2013-09-17T12:01:08-03:00',
     u'title': u'Todo es un remix',
     u'url': u'/posts/nikola/todo-es-un-remix.html'},
    {u'date': u'09/14/2013',
     u'isodate': u'2013-09-14T20:51:54-03:00',
     u'title': u'Krishnamurti, mi maestro',
     u'url': u'/posts/nikola/krishnamurti-mi-maestro.html'},
    {u'date': u'09/13/2013',
     u'isodate': u'2013-09-13T14:11:29-03:00',
     u'title': u'Econom\xeda basada en recursos',
     u'url': u'/posts/nikola/economia-basada-en-recursos.html'}]}]}
```

The `url` attribute is not the same as my json generated file (`/posts/economia-basada-en-recursos/`). I don't know why, but it contains the ".html" at the final and also says it's under "posts/nikola" (it's true in the directory tree but not in the URL)