support for ogg, webm, mp4

hi!

I changed the code, that

{{ url (without type) }} 

will generate the html

(video ...)
    (source src="{url}.mp4" type="video/mp4")
    (source src="{url}.webm" type="video/web")
    (source src="{url}.ogg" type="video/ogg")
(/video)

So it is possible to use the videos in all major browsers.