Implement versioning, automatic releases

[Andrew Ho]

As discussed in #4

It would be nice to have a version in ok.min.css like ok-1.2.3.min.css for easy identification and support for a non-moving target. I will likely put it inside a Git repo without using a CDN and for that scenario the version would be great.

Here are some integrations that help with automated releases:

• https://github.com/semantic-release/semantic-release
• https://github.com/release-it/release-it
• https://github.com/intuit/auto