Correct +combineLatest: documentation regarding completion
Merge pull request #656 from ReactiveCocoa/correct-combineLatest-documentation

Correct +combineLatest: documentation regarding completion
Clarify completion documentation for -switchToLatest & +if:then:else:
Merge pull request #662 from ReactiveCocoa/switchToLatest-docs

Clarify completion documentation for -switchToLatest & +if:then:else:
Merge branch '2.0-development' into racobserve-change-dictionary
Code comments go out of date fast.