I'd like to re-implement our bin/start script from the private Bullet Train repository, but implemented based off of Procfile.dev. The script should check whether the first entry in Procfile.dev is running, and if it isn't, do an exec call to run it. If there are any additional entries in the Procfile.dev, it should report back, so that the developer can open another window and run the script again. When there are no more entries that aren't already running, report that to the user.

We'll also need to create a rake task that serves as an installer for a bin stub in a projects bin directory that calls all this logic. (Previously we could just put all the logic in the bin file because we were distributing it with the Bullet Train repository. That doesn't work anymore, so look at bin/webpack-dev-server, etc. for examples of how to do this.)