Add Procfile.
Add .preferred_otp_version file for Erlang buildpack.
Switch of OTP R16B03.
Reorder dependencies.
Select R15B01 as preferred OTP version
Select 17.3.4 as preferred OTP version
Select R16B03 as preferred OTP version
Remove unneeded file.
Minor cosmetic changes.
Merge pull request #5 from jkakar/run-on-heroku

Add a `Procfile` and OTP version file to run on Heroku.