Keep a change log

[michaelherold]

It would be nice if there was a change log for the spec. This would help to keep up-to-date on the spec version you're using in an engine.

I'm partial to the keepachangelog.com format.

[pbrisbin]

Thanks for the suggestion, I agree. Our preferred format is mostly like that one, so I think you'll be happy with it. I will keep this on my plate and back-fill a CHANGELOG.md when I'm able -- I don't know that we've released more than the first version so far, but will certainly check.