Template the top level output

[jasinner]

As a follow up to issue #33, include the top level package in the template.

[jasinner]

Thinking about this a little more I think we also need the ability to turn off the top level package output.

[RalphCorderoy]

Can we have the motivation in addition to a proposed solution. That would allow for discussion about the need, and alternative solutions.

[twaugh]

I can now provide motivation for this.

We will want to run retrodep on a project which contains multiple separately-vendored projects (as implemented in #76), and want to track which of those projects each vendored dependency is brought in for.