FIx #4: Update bounds on change layout 

Hello first, I really like your button. I was having the same issue as #4 so I've overriden layoutSubviews to update the rippleView and the backgroundView frames. I've also added a corner radius property so as to have rounded buttons. What do you think? 

PS I updated the storyboard layout  to reflect this change when you rotate the view and made the class @IBDesignable to see the changes immediately.
PPS sorry for my bad english

![ios simulator screen shot 18 09 2014 10 29 01](https://cloud.githubusercontent.com/assets/2380325/4322645/3dea513a-3f4a-11e4-929a-00e43da56681.png)

![ios simulator screen shot 18 09 2014 10 29 06](https://cloud.githubusercontent.com/assets/2380325/4322652/4778fd1e-3f4a-11e4-8c01-8e828487f4c9.png)