Add Git tags to repository

[alerque]

I was recently trying to audit the difference between versions for fluent, and tried looking for tags to compare. Unfortunately this repo seems to have given up having tags at all some time ago, leaving us to parse through the commit log manually to guess release points.

Would it be too much to ask for Git tags here to match releases on crates.io?

If you don't have time to mess with this I'd be willing to step in like I did for assorted Fluent crates and backfill tags on the correct commits based on crates.io meta data (they store the commit hash in published releases).