Rule to validate that the bumped version has been added to CHANGELOG.md

[micahhahn]

What the rule should do:

Check the CHANGELOG.md file for an entry corresponding to the current version specified in elm.json.

What problems does it solve:

Rather similar to UpToDateReadmeLinks this rule could help package authors catch missing information they meant to add to CHANGELOG.md between running elm bump and elm publish.

We could also consider requiring conformance of CHANGELOG.md to keepachangelog.com as part of this rule. For example we could enforce the following format for entries:

## [0.3.0] - 2015-12-03

When (not) to enable this rule:

If you do not want to maintain a CHANGELOG.md and want consumers of your library to guess what has changed between versions.

I am looking for:

Mostly documenting an idea I had and trying to open a discussion around if it is a good one.

I may find the time to work on this in the near future, but if someone else wants to tackle it go for it!

[jfmengels]

Hey @micahhahn

This is an interesting idea. This is unfortunately not yet possible because elm-review doesn't give you access to the CHANGELOG. That said, there is a proposal to make this possible, so please pitch in if you want to see this made possible 😊

[micahhahn]

Ah interesting, I had assumed we would be able to just because we can touch README without really digging into the code.

[jfmengels]

READMEs are a pretty important part of an Elm package, hence why support was added for it. Had I been actively maintaining changelogs more at the time I could have added support for it. Now I think the other proposal makes a lot of sense.