Use active git user from source repo instead of user's default ID

[theoy]

Sometimes people use different git user IDs (e-mails) for different repositories.

Because this creates temporary repositories, if someone is invoking from within a repository with a custom ID, then that custom ID is not used in the new temporary repository. Instead, the default git user ID is used (global across the user's OS account).

This should default to process.cwd() if cwd is inside a repository, and provide the option to override with a custom context directory.