Feature Request: FedEx Support

[Saijin-Naib]

https://developer.fedex.com/api/en-us/catalog/track.html#/api

I'm not qualified to substantively review the API, but it looks appropriate to me.

It'd be great to have in the USA as USPS, UPS, FedEx, and DHL cover pretty much any and all "last-mile" post, with USPS being the main provider of last-mile service, even for other services.