Template: add changelog support

[rsyring]

Like pyp?

Other ideas at: https://github.com/c4urself/bump2version/blob/master/RELATED.md

[rsyring]

Coppy has started using towncrier. We could add that config to the template. Could put it behind a coppy variable if projects don't want it. It's just a folder, config file, and dependency.

refs #80