Refactor CHANGELOG.md to the Keep a Changelog style

[odow]

I'll add the preview link once it runs: https://documenter.juliadocs.org/previews/PR2035/release_notes/

There has been some discussion on Slack about package changelogs.

The general consensus was that following https://keepachangelog.com/en/1.0.0/ is good practice.

Existing examples:

• @fredrikekre's https://github.com/fredrikekre/Literate.jl/blob/master/CHANGELOG.md
• JuMP's https://jump.dev/JuMP.jl/dev/release_notes/

The JuMP release notes are slightly complicated because they are built on-demand from a simplified file:

• https://github.com/jump-dev/JuMP.jl/blob/master/docs/src/changelog.md
• https://github.com/jump-dev/JuMP.jl/blob/451740ada26f634edb09cc5ec19b2c4d48031cfe/docs/make.jl#L214-L249

I've followed the JuMP approach here. Open to suggestions/discussions for what we could do differently, and how this could be incorporated more directly into Documenter.

cc @giordano

I haven't gone through and looked up the date each release was tagged, but that would be good to have.

Ideally, we'll aim for something standard here so that other packages can copy.

[odow]

The other issue is that if you click "Edit" in the documentation, it tries to redirect you to https://github.com/JuliaDocs/Documenter.jl/blob/master/docs/src/release_notes.md. Is it possible to change the edit link for a particular page?

[mortenpi]

Is it possible to change the edit link for a particular page?

We should generate an at-meta block with an EditURL in release_notes.md.

[odow]

Added the dates with

$ git log --tags --simplify-by-decoration --pretty="format:%(describe:tags=yes) - %cs

tags ="""
# Copy-pasted output from git script above
"""
file = read("CHANGELOG.md", String);
for line in split(tags, "\n")
    tag, date = String.(split(line, " - "))
    file = replace(file, "## Version $tag\n" => "## Version $tag - $date\n")
end
write("CHANGELOG.md", file);

[mortenpi]

Alright, I think this is basically good to go. I'll just make a couple of tiny modifications.

[mortenpi]

Alright, let's get this merged. We can do any code organizational changes for re-use in a separate PR. Thanks a lot @odow, especially for taking the time to convert the existing changelog!

[odow]

This looks good: https://documenter.juliadocs.org/dev/release-notes/. We should definitely encourage packages to adopt the style.