support `--version` to output version information

I'm the maintainer of [Dorothy](https://github.com/bevry/dorothy) and we have a command called [command-working](https://github.com/bevry/dorothy/blob/master/commands/command-working) which checks if a command is working by trying ` --version` and ` --help` among other things, neither of which return an exist status of `0`, `22`, or `200`. Would be good of `--version` could return exit status `0`.

The issue provides no file or test path. Start by locating the Go CLI entry point and its existing flag handling, then run rmtrash --version; done means the command outputs version information and exits with status 0. Check for an existing CLI test location and add coverage there if one exists.

Written by the indexing model from the issue text.