Fix #927 - document .wait

[kbariotis]

Indeed, wait function is a neat one especially when messing with a lot of AJAX requests in your SUT. It should be present in the docs. We can also add some examples if you would like.

[assaf]

Sweet. Can you add something about promises, though? This method (like most others), either called with a callback, or returns a promise you have to wait on.

[kbariotis]

@assaf looks good?

[assaf]

options (required): Options that determine how long to wait (see below)

It can't be both optional and required

[kbariotis]

@assaf (sorry, that moment when you're trying to help and you're doing it worst!) updated and also clean up history.

Thank you