Compile CHANGELOG for the last 3 major versions

[IvanIvanoff]

We need to compile a continue supporting a CHANGELOG file that tracks what's new, fixed, and if there are breaking changes in every version.

Let's start with retrospectively adding what changed in versions 0.9.x, 0.10.x, and 0.11.x

Example changelog format that we can try to replicate: https://github.com/elixir-lang/elixir/blob/v1.13/CHANGELOG.md
As this project is much smaller, we can do this in a single file and not one file per major version.