HTTP APIs.
Performs a HTTP call, proxied via the server (to avoid CORS issues).
Options:
* method
: GET, POST, PUT, DELETE (GET is default)
* headers
: table with header -> value mappings
* body
: either a string or table (which will be JSON stringified)
Returns:
* ok
: boolean if the request went ok
* status
: HTTP status code
* headers
: HTTP headers
* body
: for content types:
* text/*
: string
* application/json
: parsed JSON object
* anything else: UInt8Array