Declare deliberate "async=true" on XMLHttpRequest open

On some installs, both Firefox & Chrome throws:
"Fetch failed: " DOMException [InvalidAccessError]: "A parameter or an operation is not supported by the underlying object"
Due to pre-set async=false (overridden prototype, maybe?)
This fixes the above issue.

Fix typo in npm install instructions

Improve Request/Response BodyInit consuming

I could not figure out document.cookie, so just setting the cookie to reset.

https://fetch.spec.whatwg.org/#concept-http-network-or-cache-fetch step 13, requires credentials flag to be set to accept cookies

cc @aroben

Suspect this api key was wrong