Add syntax for channels/users

[diafygi]

It would be great to add folders for specific youtubers. That way, I can just have my list of users I subscribe to in directory format. Perhaps having similar syntax to google's site:example.com syntax?

larry@localhost /tmp/ytfs $ mkdir user:zisteau

[rasguanabana]

Should appear in next commit along with preferred format selection and some other options. Also, I'm planning to implement playlist support in near future, just have to think about how :)