Add support for JSFiddle username

I know this plugin won't make it to 3.0 but this has been a useful change for me.

This change allows support for including a users JSFiddle username to be used like so:

```
{% jsFiddle 7GvV2 result,css,html %}
{% jsFiddle i-like-robots/7GvV2 result,css,html %}
{% jsFiddle i-like-robots/7GvV2/5 result,css,html %}
```

Currently attempting to embed a version without a username will get a 404, E.G.

http://fiddle.jshell.net/7GvV2/show/ (fine)
http://fiddle.jshell.net/7GvV2/5/show/ (404)
http://fiddle.jshell.net/i_like_robots/7GvV2/5/show/ (fine)