Add support for Wait to accept Question, Resolution pairs.

[perrygoy]

I keep finding myself wanting to say something like:

the_actor.will(
    Wait.until_the(Number.of(BALLOONS), IsEqualTo(5)
)

But it can't! I think it would be nice to add it.

Things we'd need to do:

• Add new until and until_the methods to accept a Question and Resolution pair.
• Add handling in the log_message property to properly describe what we're waiting for.
• Add a check in the try block of perform_as to either do what it does now or pass the Question, Resolution pair to a Silently(Eventually(See(...))).
• Add tests for that!
• Add documentation for that!

[bandophahita]

I'm super torn about the names of these.
I could see how someone fresh to screenpy could easily be confused by Wait vs WebDriverWait. That said, I like Wait.until because it makes the most sense to me.

[bandophahita]

It feels proper to point out that the following two statements are functionally equivalent. (maybe in documentation?)

actor.will(Wait.until(Number.of(BALLOONS), IsEqualTo(5))
actor.will(Eventually(See(Number.of(BALLOONS), IsEqualTo(5))))

Though, I imagine we're going to want the output logging to look different.

[perrygoy]

Yeah, i'm thinking about expanding the Wait Strategies section of the documentation with a bit talking about connotation of those two approaches. Plus i'm pretty sure behind the scenes the first will be doing the latter, haha.