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.