RFC: snap on networkIdle

[cdaringe]

problem

I want to capture, but my readiness conditions are >1, and a bit complex. Current APIs do not serve my needs well.

discussion

pup allows for detecting networkIdle conditions. This is the best sigil that my app is ready to go (perhaps plus a few ms to finish processing any network activity).

Perhaps we could expose more ways to detect readiness? Perhaps the most flexible would be a callback function that allows me to do stuff with the page object, such as invoking .waitForNetworkIdle