Inline buildpack

This is a buildpack for projects that wish to build themselves and is partially based on https://github.com/kr/heroku-buildpack-inline

First, it checks if there is a provision directive on devstep.yml under the project's root and it uses the instructions provided during container provisioning.

For example:

provision:
  - ['configure-addons', 'redis']
  - ['configure-addons', 'heroku-toolbelt']

Will configure the Redis and Heroku toolbelt addons.

If no provision instructions are found, the buildpack will look for an executable file under bin/compile of the project root and will run the script if found.