Private modules

[kpcyrd]

While it's possible to drop custom scripts into ~/.local/share/sn0int/modules/ we should explicitly support private modules. This could conflict with the registry and #8 though.

We could improve support by allowing the user to clone a repo into sn0int/modules/foo/. If we discover a git repo at sn0int/modules/foo/.git we would exclude it from a regular update and instead try to fetch+fast-forward the repo.

We could also invoke git clone for the user if we detect an url argument for sn0int install.

[kpcyrd]

With regards to the scripting guide it might be best if we support registering some paths as namespace in the config file. Those are then considered private.