* Use node-fetch instead of xhr
* Remove XMLHttpRequest.js
// FREEBIE
* Avoid calling json() on non json responses
Previously we would catch and swallow JSON parsing errors resulting from an
empty response, though empty responses are normal from a few endpoints, like
requesting sms or voice registration codes.
Since the JSON parsing call is now handled internally by node-fetch, we have to
keep closer track of our expected response type to avoid throwing an exception.
// FREEBIE