`--since` option not applied when used together with `--authors` option about git-stats

[j67678]

https://acassis.wordpress.com/2009/07/16/getting-git-revision-by-specific-date/

[IonicaBizau]

@renzhn Thanks amazing point! ✨

Currently this is not supported, but it would be neat to be supported.
This should be implemented here, like you said using since and until. 🎇

[j67678]

@IonicaBizau Also I noticed git shortlog counts each author's commit, not lines of code. I think this should be clarified as users don't know how contributions are counted.

[IonicaBizau]

@renzhn True. I guess this is how GitHub sorts the repo contributors as well (the more commits you have, the higher in top you are). Obviously, we should improve the docs in this direction. 📝