title: Heroku Context Auto Building with Github
body: <p>Does Heroku supports context building like Openshift supports? Like, i have this repository but i want to build only inside a specific folder in github webhook. 
  I coud not find anything in interface and for CLI i just could find resources using the heroku-git. It needs to be IN THE GITHUB WEBHOOK, is there anyway to do that? The method for commit to a heroku origin is not what i'm looking for. </p>