Add facebook plugin

[mbajur]

No description provided.

[rb2k]

Thanks!
It seems like test_facebook() seems to fail in that travis run. Did it pass locally for you?
Maybe it's because of different headers during the download attempt OR you'd have to set the :method option to GET instead of the default HEAD.

[mbajur]

Ok @rb2k , it was caused by the fact that facebook video url needs to be put between the brackets (when using viddl-rb shell command, ampersands are not parsed well without the brackets). I've also added SSL urls support for specs cause the ones coming from facebook have https:// prefix.

[rb2k]

Since your other PR was accepted, it seems like you'll have to rebase this on master so it can be merged

[mbajur]

Well, that was actually first rebase in my life so i'm not sure if i've done everything right. Hope so.
Sorry for the troubles!