Adds an `unindent()` function that strips common leading indentation
from strings, and apply it to integration test case strings, so that they
can be written in a more readable style.
Just's dependency on brev was the cause of a
fairly deep branch of the transitive dependency
tree. To decrease build time and make the life of
packagers easier, this diff moves the functionality
that Just was using in Brev into Just itself, and
removes the dependency on Brev.
Fortunately, the only functionality that Just was
using was the output function and OutputError
enum, so this was easily done.
