title: smooth rounded corners in swift
body: <p>How can I create a UIButton with rounded corners that are smooth? 
  The standard apple rounded corners are much nicer than the standard rounded corners. 
  If I design a button in sketch, I can toggle "smooth corners" which toggles the corners of a shape from Apple rounded corners (smooth) to standard rounded corners.</p>
  
  <p>Here is a comparison: </p>
  
  <p><a href="https://i.stack.imgur.com/82g7Z.png" rel="noreferrer"><img src="https://i.stack.imgur.com/82g7Z.png" alt="enter image description here"></a></p>
  
  <p>How can I toggle this in swift?</p>
  
  <p><code>showContentButton.layer.cornerRadius = 20</code> rounds the corners, however, I don't really know if this rounded corners are "smooth corners" or "standard rounded corners". And I don't know how to toggle this. Any ideas?</p>