This allows direct introspection of `version.plist` files from zip
archives, such as the autopkg source zip downloaded by
`AutoPkgGitMaster.nupkg.recipe` from GitHub.
For zip files only, Versioner can also now optionally ignore a single
root directory, which faciliates content extraction from sources such as
GitHub source archives, which have a root directory:
`user-project-truncatedhash`. Since it's extremely difficult to know the
truncated hash ahead of time, `skip_single_root_dir` will interpret any
path as relative to it.
An exception is raised if there is more than one root directory in the
archive and the flag is set.
Elliot Jordan
Brian Smith
Michal Moravec