NEW: gogrepo, a downloader for games from GOG.com

Hi,

New port for downloading GOG.com games via the command line. Useful
especially for a potential future game library management system...

Works, tested both py- and py3-. Passes make-port-lib-depends-check and
portcheck.

I don't have much experience with python ports yet. I used net/py-dpkt
as a starting point.

A few more points about the port:

- there are no release published, but the gogrepo.py calls the version
0.3a. That's why I chose 0.3apl20190727 for MODPY_EGG_VERSION. I am
not 100% sure if the "a" will work well with our versioning, but
since games/cataclysm-dda uses "0.D" in DISTNAME, this seemed ok.
Please correct me if this assumption is wrong.
- uses a launch script that calls gogrepo.py
- examples for init, download etc here [1]

comments, ok's?

[1] https://github.com/eddie3/gogrepo