Multi package linting

This should fix #68. I still want to figure out if it is a problem that foo and foo_test are linted together but I would also like to hear your feedback if this is an OK direction.
I think the instruction for using just a single package should be dropped in this PR as well. In #68 the usage <code>golint *.go</code> is mentioned which would be possible then. Golint would then "just work" no matter what you throw at it (ok the "..." wildcard would be still missing for paths but I have that on my open source TODO).