[placeholder issue] for recording old crate removal commit hash

[matthiasgoergens]

Commit 0a40721 from #89 broke singer-pro. In #314 we removed it temporarily.

This issue is here as a place-holder to remind us that we want to eventually restore the package.

TODO(Matthias): post instruction for how to do that, once the PR is merged, and we thus have a commit hash I can use in the instructions here.

Originally posted by @hero78119 in #314 (comment)