响应编辑通知
textViewShouldBeginEditing(_:)
textViewDidBeginEditing(_:)
textViewShouldEndEditing(_:)
textViewDidEndEditing(_:)
响应文本更改
textView(_:shouldChangeTextIn:replacementText:)
textViewDidChange(_:)
响应URL
textView(_: UITextView, shouldInteractWithURL: NSURL, inRange: NSRange) -> Bool