Maintain changelog and have tags

[sb10]

I appreciate the workflow is under active development, but by necessity we are using it production.

It would generally be useful to have a CHANGELOG.md in the format of http://keepachangelog.com/.

It would also be valuable to start version tagging master (to correspond to each section of the CHANGELOG.md), so that those using the workflow in production can pick a version to use and easily understand what that version comprises, and decide if and when they should go through an update process.

Since it's used in production, I'd propose starting with v1.0.0 now, and incrementing the version as per http://semver.org/ rules for each merge to master. Major version would change if there are any backwards-incompatible changes to parameter names or meanings.

[m-bull]

Thanks for the helpful links and advice. As I've merged a large quantity of PRs today and made some decent refactors on top of those to preserve the readability and style of the workflow, I guess now is a good time to start this.

[mgcam]

Would be nice to start using tags.