GET /profile/<username>

This API is really useful, and I thought it would be cool to add a `GET /profile/<username>` endpoint for getting user profile details & anime/manga stats. Let me know if this seems reasonable!

Here's an example response (for `/profile/xinil`):
```json
{
   "avatar_url":"http://cdn.myanimelist.net/images/na.gif",
   "details":{
      "birthday":"March  4, 1985",
      "location":"California",
      "aim":null,
      "msn":null,
      "yahoo":null,
      "comments":816,
      "forum_posts":9302,
      "last_online":"Yesterday, 3:09 PM",
      "gender":"Male",
      "website":"http://myanimelist.net",
      "join_date":"November 5, 2004",
      "access_rank":"Site Administrator",
      "anime_list_views":187283,
      "manga_list_views":2538768
   },
   "anime_stats":{
      "time_days":118.1,
      "watching":6,
      "completed":220,
      "on_hold":9,
      "dropped":86,
      "plan_to_watch":53,
      "total_entries":374
   },
   "manga_stats":{
      "time_days":21.7,
      "reading":14,
      "completed":12,
      "on_hold":3,
      "dropped":21,
      "plan_to_read":25,
      "total_entries":75
   }
}
```