https://pbrisbin.com/posts/parsing_database_url/
https://haskellonheroku.com/tutorial/
https://github.com/mfine/heroku-buildpack-stack
https://github.com/haskell-servant/example-servant-persistent/blob/master/src/Models.hs
https://devcenter.heroku.com/articles/add-on-partner-api
https://devcenter.heroku.com/articles/add-on-manifest
https://stackoverflow.com/questions/24821364/how-to-store-an-enum-adt-in-persistent
https://stackoverflow.com/questions/30062707/foreign-key-constraints-in-yesod-persistent
https://github.com/heroku/kensa