By definition of strings.Split(..., sep) it "slices s into all substrings
separated by sep and returns a slice of the substrings between those
separators". That means that

    string.Split("hello\nworld\n", "\n") -> ["hello", "world", ""])     # NOTE the last ""

when parsing file by lines, it is handy though to do not get last empty
"" after last "\n". #6 shows how we missed to do that filtering-out for
case of empty backup.refs file and errored-out because of that.

To fix let's introduce a helper - splitlines(), which does the job of
filtering-out last empty entry after last separator. By using this
helper everywhere we can hopefully avoid problems while pulling only
empty repositories (#6 case), and also similar ones.

Fixes #6
/reported-by @iv