Improve human-friendly output.

Since most packages are under vcs, display only those that aren't with
"?" symbol, instead of using "@" to indicate presence of vcs.
Add DebugPresenter, available via --debug flag.

It includes verbose output for debugging purposes.
Add RootPath field to DebugPresenter.
Rename local vars.
Merge pull request #14 from shurcooL/dev

Improve default human-friendly output.