UPM support

[starikcetin]

Can we introduce UPM support to be used with https://github.com/mob-sakai/UpmGitExtension? I can do it for you if you don't have time.

[starikcetin]

I made it, it is working: https://github.com/starikcetin/uREPL

If you create an orphan branch named upm here, I can send a pull request.

@hecomi

[hecomi]

Thank you very much for supporting UPM for uREPL. It would be very helpful for all users!

I think it's possible to send PR without my work in this repository. Just fork this and create a branch from the latest commit, then commit files related to upm support and send PR from GitHub web.

[starikcetin]

We need a separate branch for UPM, since the file structure is different. I can't send a PR without the branch already existing here as far as I know.

[hecomi]

Sorry, I hadn't checked the manner of the official UPM and the branch strategy of UpmGitExtension... Instead of orphan branch, I created a subtree: https://github.com/hecomi/uREPL/tree/upm