Support for binary content

[keroami]

3rd party provides me with large gzip'ed json.

Add

@external(javascript, "../ffi.mjs", "read_body")
pub fn read_body(
  a: Response(FetchBody),
) -> Promise(Result(Response(BitArray), FetchError))

which the user must gunzip afterwards?

If so, I have a PR.

[lpil]

Good idea! Let's call it read_bytes_body.

[keroami]

I built it all, only to realize I didn't use it - the download mechanism of the run-time (now, at least) takes the 'encoding: gzip' and gunzips for me, yielding a String.

Nevertheless, there could be other binary downloads (images, zip files) that would need this.