get contributor names from Dist::Zilla metadata

Main objective: fetch contributor names directly from Dist::Zilla metadata `x_contributors`.

In writing this code, I also found and fixed a bug, and made a few other small changes and refactorings :)

Since there are no tests, I tested a build against a few other dzilfied distributions and everything looks good.

(I'd still like to write some tests though. It's amazing how few other Pod::Weaver dists have tests for me to steal from!)