Respect loaded

closes #28 (https://segment.zendesk.com/agent/#/tickets/16767), still needs some testing.
pulling this here to see what you guys think.

cc @ianstormtaylor  @lancejpollard 
edge case, but I think we need to set `tid` to the result of this `setTimeout` so that we don't get multiple callbacks? looks like the `var` was already setup for it and the clearing looks good otherwise, so I think it's just a typo. definitely a mind-bender haha.