Group changelogs by change level instead of by date

[HonkingGoose]

What feature would you like to have?

Group changelogs by change level instead of by date.

I showed @Belco90 a example of bad/malformed input over on issue #66:

https://octoclairvoyant.vercel.app/?repo=facebook%2Fdocusaurus&from=v1.0.3&to=latest

He replied:

By the way: the example you attached is not grouping the different levels of changes properly. It's receiving the changes headings in a non-expected structure, so I think that should be also improved to get the changelog grouped by change levels instead of by date (as it is now).

I think the "group changelogs by change level instead of by date" deserves its own issue. 😉

What problem will be solved by having the feature?

This will probably help display the changelogs in a sensible order.

Do you want to help making the feature?

I don't know enough code to make the change.