GifHub by QRohlf

Adds support for gifv/webm/mp4 to discussions on <a rel="nofollow" href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/18292d9c1899dd2b453ea9e3c1375587569f07a1d91694af6d865f8eab086cdb/http%3A//github.com">github.com</a> Homepage: <a rel="nofollow" href="https://prod.outgoing.prod.webservices.mozgcp.net/v1/56c90633b2242083bb41c622bbeccd346527d6806a318a3a928a116e7e69dd33/https%3A//github.com/qrohlf/GifHub">https://github.com/qrohlf/GifHub</a>