timeout support

[jenni-divvito]

Hi there,

I'd really like to see support for timeouts in the lib, currently if the user has a dodgy wifi connection when using the client that causes requests to send indefinitely (but not actually fail), they end up stuck in place.

Seeing as it looks like you are just using XHR, it should definitely be doable, right now I have to use a dodgy workaround with Promise.race()