Trawl the ReactiveCocoa repo for common assertions

[lawrencelomax]

There are a bunch of different behaviours that the ReactiveCocoa repo checks in Unit Tests other than checking values sent. I've seen some tests on the number of subscriptions that occur and disposal.

I might take a look at rewriting some of the RAC Unit tests using LLReactiveMatchers, but I want to prevent this from being anything other than an experiment to figure out how suitable LLReactiveMatchers is to the task.

[lawrencelomax]

There are some commits for this on the reactive-matchers branch of my fork.