Support VCS as an option for Sourcehut and fix mercurial url

[eveeifyeve]

Hi there when I was doing nix-community/nix-init#184 there is an issue with imputing a mercurial url, It should be fetchFromSourceHut, but it's:

> nurl -p https://hg.sr.ht/\~ehmry/nim_lk
{"args":{"url":"https://hg.sr.ht/~ehmry/nim_lk"},"fetcher":"fetchgit"}

Also this tool should add the option to detect the vc tool used and output it only for sourcehut.

[eveeifyeve]

I tackled this slowly, this issue is with SimpleFetcher doesn't accept two types.