Add -[RACSignal waitUntilCompleted:] for blocking until termination

Completes #187.
Add methods to spin the run loop recursively while waiting for events
Tests for run loop spinning methods
Only set result/error/success if `done` is not already set
Add foldr implementation

Add a lazy foldr implementation and tests for it. The lazy foldr uses an
RASequence to wrap the lazy computation while making it easy to
retrieve.
Add any function

Add any function using the previously implemented foldr.
Add tests for the any function.
RAC() to the most descendant properties possible
Document the relationship of -sequenceMany: to -flattenMap:
-flattenMap: examples with operators applied after/within
Change RACPropertySubject to inherit +subject constructor instead of using it's own.
Change _itemsInFlight to an int32_t. Fixes armv7 misalignment.
Merge pull request #346 from joshvera/fix-raccommand-items-in-flight

Change RACCommand's _itemsInFlight type to int32_t. Fixes armv7 alignment.
Add type information to the RAC() macro

Should prevent issues like #344.
Add back +property, test them both.
Refactor fold interface
Merge pull request #345 from ReactiveCocoa/fix-racpropertysubject-constructor

Change RACPropertySubject to inherit +subject constructor.
Merge branch 'master' into wait-until-completed
Merge branch 'wait-until-completed' into asynchronous-waiting
Clean up duplication in -asynchronouslyWaitUntilCompleted:
Fix thread safety of -[RACSignal concat:]