milestone 2 complete

internal/git/objects.go

@@ -203,3 +203,8 @@ func (gb *GitBackend) GetCommit(sha string) (*object.Commit, error) {
 
 	return commit, nil
 }
+
+// HashFromString converts a string SHA to a plumbing.Hash
+func HashFromString(sha string) plumbing.Hash {
+	return plumbing.NewHash(sha)
+}