refactor git-autograder to generalize bebavior and reduce indirections#21

SAN-MUYUN wants to merge 7 commits intogit-mastery:maingit-mastery/git-autograder:mainfrom

SAN-MUYUN:refactor/generalise-behaviorSAN-MUYUN/git-autograder:refactor/generalise-behaviorCopy head branch name to clipboard