Add a CHANGELOG

[omid]

Have a CHANGELOG.md and log the changes.
I don't know what you've added to which version now.

[davysson]

We have a changelog for each release here: https://github.com/oxidizer-rs/oxidizer/releases

[omid]

I think having a CHANGELOG.md is better, since you can version it and change it, for example, you decide to add some ref links for "Added custom types for fields".
Or you want to prepare the changelog for the future release. I can see what I will get in the future, and also you'll not miss any changes and also every PR will also come with it's changes in the changelog (if it's needed!)