[pkg-go] Bug#811565: [uscan] git mode: allow for scanning repositories without tags

[Shengjing Zhu]

Hi,

I want to know if it's still possible to support GitHub's commit via
different way, rather than do a `git clone`.

I find GitHub has RSS feed for the commit, the url is like
https://github.com/Debian/dh-make-golang/commits/master.atom
So uscan can parse that xml feed, and get the commit data, id, and
finally forms the download link like
https://github.com/Debian/dh-make-golang/archive/71736daa55a06e466cdcc6c0347f5b9489471fe3.tar.gz,
and the version is 0.0~git<date>.<short commit id>
Besides, the RSS feed url is not an API url, and will not have the API
rate problem.

That's simpler than doing `git clone` locally, though the shortage is
site specific.
BTW, gitlab also provides such feed, the url format is like
https://gitlab.com/inkscape/inkscape/commits/master?format=atom

Thanks
Shengjing Zhu