Add RACCommand support to UIAlertView
Improve docs for UIAlertView.rac_command.
Clean up UIAlertView+RACCommandSupport.

Also adds a warning if the delegate is non-nil when hijacking.
Document that UIAlertView.rac_command overrides the delegate
Unset alert view delegate when unsetting command.
Improve docs for UIAlertView+RACCommandSupport.
Unset the associated object when unsetting the delegate
Merge remote-tracking branch 'origin/2.0-development' into hh-uialertview-raccommandsupport

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa.xcodeproj/project.pbxproj
Rewrite UIAlertView support to use delegate proxy
Update alert view tests to match implementation
Remove +printBacktrace, shorten +captureBacktrace…
Document how to use RACBacktrace on OS X
Expose rac_ GCD functions for iOS, explain them
Describe how to use RACBacktrace in the debugger
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