Add control tests for ReplaySubject

Control tests to ensure ReplaySubject's send(subscription:) behaviour matches that of PassthroughSubject

Add control tests for ReplaySubject

Control tests to ensure ReplaySubject's send(subscription:) behaviour matches that of PassthroughSubject

Add control tests for ReplaySubject

Control tests to ensure ReplaySubject's send(subscription:) behaviour matches that of PassthroughSubject

Beta 5: ReplaySubject temp-fix

Changed TestableSubscriber recorded property names

Updated for Xcode 11 beta 4

Updated for latest Combine beta API

Fixed non-standard cancellation behavior

Cancellation shouldn't call completion. More here: https://twitter.com/millenomi/status/1137382877870510080

README.md updates

Documentation tweaks