title: Providing customers with domain aliasing
body: <p>Currently I have an app which gives my users a custom subdomain.</p>
  
  <p>neat.coolapp.com</p>
  
  <p>However, I want my users to be able to CNAME their personal domain to that website.<br>
  ex. hey.neat.com -> neat.coolapp.com</p>
  
  <p>Is this possible on heroku? </p>
  
  <p>Thanks in advance for any insight.</p>