Add `gits()`: like `git()` but silently

Also replaces `git()` + exception blobs with `gits()`.
Print branch/ref info
Merge branch 'feature/ref' into develop
Separate file_name and rel_file_name

Since use of file_name as relative path introduced lots of
confusion.

This also corrects output of gitlink: file mode 'g' instead of 'd'