Make sure new selection is visible when swiping text view

Loving the work you've done with swipe/gesture navigation stuff on UITextField/UITextView. 

Possibly made a change that could be useful. When swiping a UITextView it'll scroll to make sure the selection is visible.

It's done by returning the selection range from the advance/back methods and using `-[UITextView scrollRangeToVisible]`. Writing this just now, I did realise that UITextView has its own `selectedRange` which could have been used instead of what I've done, don't think I'm knowledgable enough to know whether there are any downsides to either though.