No webm support.

[Oatwalker]

Webm's on 4chan cause the program to fail the entire thread. Would you please add support for webm?

[Dhole]

Hi,

I haven't touched the code for a while. I wrote it a long time ago and it's a bit messy (and I believe it requires a good amount of refactoring).
I don't currently plan to continue working on it, but feel free to send me a pull request with the fix.