Non-ascii characters are allowed in tags

[MrCreosote]

Thanks very much for this library, it's exactly what I've been looking for

Per the docker docs, tags must be ascii-only: https://docs.docker.com/reference/cli/docker/image/tag/

The tag must be valid ASCII and can contain lowercase and uppercase letters, digits, underscores, periods, and hyphens

But docker-image-py allows non-ASCII characters:

In [27]: parsed = reference.Reference.parse("yay:ɰoo")

In [28]: parsed["tag"]
Out[28]: 'ɰoo'