New feature: Amp-facebook-comments

[muinh]

Hi. I'd like to thank you for this library. You saved me a lot of time including the fact that it works in a proper way.
It would be nice to see amp-facebook-comments in new versions.
Now there is a case when I'm adding facebook iframe with comment inside. It converts the iframe to and shows not comment but facebook page with src in iframe pointing on it.

Now I'll write a custom solution. Maybe, if it works great, i'll make a PR, if you want ofc.