Add `background` stanza example and various cleanup tasks.

This provides missing examples for the `background` stanza as requested in #57.

I also moved all the scripts under incoming to a Makefile. The script will look for a cabal sandbox config in the parent dir to build the examples against the sandbox package db. The resulting keter bundles are dumped into ./incoming as the documentation suggests. I would also like to move all the examples under bundle/* here as well.

I don't want to impose this workflow on anyone (is everyone using sandboxes to test?). However, I had a hard time building a few of the examples so I thought this would help.

I *did* remove the `hello` (foo 0.4) executable from the cabal file, though. For one, it did not build for me (I fixed that). It just seemed to make more sense to handle all the incoming examples the same. That example now builds as part of the incoming bundles so we can verify the older configuration.

I did various other code cleanup tasks but I am not attached to them by any means.