Add EXTRuntimeExtensions.m to the UIKit test host target.
Refactored RACPropertySubject and RACBinding to have more general initializers.
Refactored RACObservablePropertySubject to use the superclass initializer.
Refactored RACObservablePropertyBinding to use the superclass initializer.
Added rac_bindingForControlEvents:keyPath:.
Require a `nilValue` since many controls have primitive properties.
Added binding to UITextField.
Added binding to UISlider.
Added binding to UISegmentedControl.
Added binding to UISwitch.
Added binding to UIDatePicker.
Added binding to UIStepper.
Use -set...:animated: methods where available.
Merge branch '2.0-development' into uikit-bindings

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa.xcodeproj/project.pbxproj
Added UIKit bindings to the change log.
Use an empty string as the nilValue for UITextField.
Reindent the complex signal.
Add commas to improve readability.
Rename the backing subject and document it clearly.
Make RACPropertySubject a subclass of RACBinding to get rid of duplication, get rid of the hacky +alloc without -init.