Baneby

• Renames RxTests library to RxTest because of problems with Swift Package Manager.
• Adds Swift Package Manager support
• Adds Linux support
• Replaces AnyObserver with UIBindingObserver in public interface.
• Renames resourceCount to Resources.total.
• Makes rx.text type consistent with UIKit String? type.

textField.rx.text          // <- now has type `ControlProperty<String?>`
textField.rx.text.orEmpty  // <- now has type `ControlProperty<String>`

• Adds optional overloads for bindTo and drive. Now the following works:

let text: Observable<String> = Observable.just("")

// Previously `map { $0 }` was needed because of mismatch betweeen sequence `String` type and `String?` type
// on binding `rx.text` observer.
text.bindTo(label.rx.text)  
   .addDisposableTo(disposeBag)

...

let text = Driver.just("")
text.drive(label.rx.text)
   .addDisposableTo(disposeBag)

• Adds trim output parameter to debug operator. #930
• Renames NSDate to Date everywhere.
• Renames scheduler init param globalConcurrentQueueQOS to qos and removes custom enum wrapper.
• Adds setter to rx property to enable mutation of base object.