Fix normalize_paths to allow whitespace

This fixes normalize_paths so that it strips whitespace before and after
paths before working on them. This allows you to do specify excludes
with multiple lines in the config file.

This also tweaks normalize_paths so that the behavior matches the
docstring.

This also adds tests.

Fixes #339
Add a few more cases of "not value"
Add Ian to list of maintainers.
Update changelog for issue #339 / #343
Merge branch 'willkg:normalize_path_fix'

Pull request #343, Issues #339 / #343