tag a release

[bwalex]

Any chance you could tag a release? coreos/rkt much prefer to only depend on tagged projects (see rkt/rkt#2428). As they put it:

Please consider assigning version numbers and tagging releases. Tags/releases
are useful for downstream package maintainers (in Debian and other distributions) to export source tarballs, automatically track new releases and to declare dependencies between packages. Read more in the Debian Upstream Guide.

Versioning provides additional benefits to encourage vendoring of a particular (e.g. latest stable) release contrary to random unreleased snapshots.

Versioning provides safety margin for situations like "ops, we've made a mistake but reverted problematic commit in master". Presumably tagged version/release is better tested/reviewed than random snapshot of "master" branch.