This is a fork of developit's unfetch package

The fork was created to support these following features:

• Allow fetch calls in the browser to use Headers as their options.headers, instead of being limited to only a JavaScript object literal.
  • Headers instances CANNOT be iterated like simple JavaScript objects correctly (since they are Iterators), and must instead be iterated over using a native (not transpiled) for...of loop, or iterated over "by hand" using a while loop by leveraging the lower level Iterator data structures.