feat: monorepo support

[aa900031]

Making changelogen support monorepo. Although there is another PR (#45) that does the same thing, it doesn't seem to be maintained anymore.

Under monorepo mode, the following will be done:

• Search for all packages
• Generate tags for each package (e.g. @awesome/pkg@1.0.0) and get the commits for that package
• If there are no commits, do nothing
• If --bump or --release is set, update the version of each package
• Generate a CHANGELOG.md file in each package directory.

I think this cloud be resolve #18, config for commit can resolve #82

[pi0]

Thank you so much for working on this PR dear @aa900031. It really looks good overall while was checking changes. However since this is a rather big feature in changelogen, it would be nice if we could split down the problem and progressively implement if you don't mind. I have made #85 to track (your help is more than needed on this!) also closing your current pull request as I'm worried it can quickly get into merge conflicts if we don't break it down.