Add the ability to control the build number via a script or command

The build number that is being used is really just _either_ the run number or the iteration number, whichever is greater. Unfortunately, this really isn't unique in any way. As such, we need one of two things:

1. A better hashing function for run number/build number that is _serially increasing_;
2. A way for the user to specify their own way of determining a build/run number.