Support parsing commits

[gardar]

It would be useful to have a additional option to parse commits since last release instead of pull requests.

So instead of parsing the labels of the pull requests it would parse the commit messages where the commits would need to follow the conventional commits standard.

I've already got a few projects where we parse the the commits like this and add them to the release notes and also use them to determine the semantic version, it would be great if antsichaut would fit into that workflow.

[rndmh3ro]

That would probably be a good addition! :)

I'm not currently using commits for the changelog, so if anyone wants to implement it, feel free!