Allow setting custom defaults for async timeout and poll interval

[mjbeauregard]

Fixes: #255

In some cases (e.g. when running on slower machines) it can be useful to modify the default timeout and poll interval values like this:

// Swift

// Increase the global timeout to 5 seconds:
Nimble.Defaults.AsyncTimeout = 5

// Slow the polling interval to 0.1 seconds:
Nimble.Defaults.AsyncPollInterval = 0.1

[mjbeauregard]

Note that we are still testing this PR in a real project and the results are mixed. For a few days we thought we had solved the problem, but are seeing timeout errors again today which is getting really frustrating. I will follow up again after more testing.

[jeffh]

Have you tried looking at the CFRunLoop to see what timers you have attached at the point of failure?

The PR looks good to me, although I just merged in support for bleeding edge swift that moved files around and broke the mergability of the it.

I'll have some time after this week to try and resolve the merge conflicts if you don't get around to the PR.

[pivotalstitch]

Can someone please specify what a polling interval is? Also, how would one use this?

[mjbeauregard]

Given the expression:

expect(someValue).toEventually(equal("blah"), timeout: 5.5, pollInterval: 0.2)

Nimble will repeatedly evaluate someValue every 0.2 seconds until it equals "blah" or until it times out (after 5.5 seconds, at which point the test will fail).

[modocache]

Thanks, @mjbeauregard! 👍

I'd happily merge pull requests to add docblocks to the public symbols in AsyncDefaults, as well as to expand the documentation on methods like toEventually. Strikes me as a potential point of confusion for users, who shouldn't be expected to know how async matchers poll their expectations.