Add a release script

The Makefiles were mostly filled with a complex shell script written in
m4sh. Moving that out into a separate script helps debugging and
compatibility, and in general makes life better.
Should we just recommend that the Debian building, pushing, etc. just be done as a completely separate process? I think at this point, it's confusing as to whether all of these steps should be done at the same time, separate machines, or what.