Method from_git

tools/backport.py:89–92

(self, *args)

    @classmethod
    def from_git(self, *args):
        result = run(["git", "log", "--oneline", *args], capture_output=True)
        lines = result.stdout.splitlines()
        return CommitHistory(lines)

    def __init__(self, lines):
        commits = {}