Move the state tracking variables in RACObservablePropertyBinding to a thread local storage for thread-safety.
Merge remote-tracking branch 'origin/2.0-development' into thread-local-stack-counter
Switch to using an array instead of a dictionary for performance.
Merge remote-tracking branch 'origin/thread-local-stack-counter' into thread-local-stack-counter
Merge branch '2.0-development' into thread-local-stack-counter

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/RACObservablePropertySubject.m
Use for loops instead of getting the index even when we don't need it.
Use -indexOfObjectPassingTest: in destroyCurrentThreadData.
Break out early if we don't need to create the data wrapper.
Be less stingy with vertical whitespace.
Removed unnecessary parens.
Merge pull request #671 from ReactiveCocoa/thread-local-stack-counter

Use thread safe KVO stack counter in RACObservablePropertySubject.
Capture all major breaking changes
List some minor breaking changes as well
List major non-breaking improvements
Uppercase for consistency
Don't use bullets for single items, fix C string section
Add TOC
Copy the introductory text from #618
Merge branch 'add-changelog' into cleaner-backtrace-retrieval
CHANGELOG