Trivial enhancement: All commands which require an author should accept --author

[Ulrich Gemkow <ulrich.gemkow@xxxxxxxxxxxxxxxxxxxx>]

Hello,

A trivial enhancement request:

All commands which require that the author is set (and complain if
it is not set) should accept the option --author.

At least the command stash does not accept this option. We are using
git version 2.17.1 (Ubuntu 18.04).

Thanks for the great work!

Best regards

-Ulrich

-- 
| Ulrich Gemkow
| University of Stuttgart
| Institute of Communication Networks and Computer Engineering (IKR)