Adding webfonts to proxied file extensions

Webfonts won't be rendered without a matching `Acces-Control-Allow-Origin` header. `raw.github.com` will serve these with `Access-Control-Allow-Origin: https://render.github.com`, so we can't redirect font requests.

This is breaking FontAwesome. See an example of this breakage in https://rawgithub.com/sapo/Ink/develop/dist/documentation/icons.html#nav-web