Improved logging and detection of dead processes

Hello,

I came across foreman trying to find a simple way to run multiple processes inside docker containers with the same guarantee of Foreman that once one of the Procfile defined processes exits (or is killed), Foreman will kill these processes. I added this functionality and improved logging in a way that resembles that of Foreman itself.

I added some test and they all seem to pass in Fedora 20 and my Mac. Let me know what you think.

Thanks for your work in Shoreman, it's been very helpful to me.