Allow to run_copy to specify a subdirectory

[Kumzy]

Actual Situation

Hello,

I would like to host all the templates in a single repository. My current way of doing it is by creating different directories.

Each one store a different template. I know it's not the recommended way that copier suggest but I have no use of the update function at the moment.

Maybe there is a different way or better approach to do this.

Desired Situation

I would like to be able to copy the content of a subdirectory (of a github repository set in src_path) inside the root directory of the destination path

Proposed solution

I would like to be able to specify a subdirectory parameters in the run_copy method