Added Coursera class
Use `SEL` variable in RACSwizzleRespondsToSelector
Replaced interval+take1+subscribeNext with afterDelay
Add -[NSUserDefaults rac_channelTerminalForKey:]
RACSequence addition added to NSIndexSet
Remove unused variable
Don't send signals back when sent from the other side
Reive notes taken into account, small odds fixed
NSIndexSet sequence additions TestSpec fixed according to Notes
Style: spaces around BOOL
Merge pull request #1010 from ikesyo/swizzling-use-selector-var

Use `SEL` variable in RACSwizzleRespondsToSelector
Expect BOOLs, not NSNumbers
Add NSUserDefaults+RACSupport.h to ReactiveCocoa.h
Merge pull request #1018 from ReactiveCocoa/user-defaults

Add an extension to `NSUserDefaults` to create a channel for a key
Make NSUserDefaults+RACSupport.h public
Merge pull request #1021 from ReactiveCocoa/fix-user-defaults-header

Make NSUserDefaults+RACSupport.h public
Make NSUserDefaults+RACSupport.h more public
Merge pull request #1022 from ReactiveCocoa/fix-user-defaults-header-more

Make NSUserDefaults+RACSupport.h more public
Remove extraneous newline
Merge pull request #1005