Add todo mode and replace the plan with TODO.md

internal/git/git.go

@@ -236,6 +236,18 @@ func Head(dir string) (string, error) {
 	return run(dir, "rev-parse", "HEAD")
 }
 
+func ReadFile(repo, rev, path string) (string, bool, error) {
+	_, _, code, err := runCode(repo, nil, "cat-file", "-e", rev+":"+path)
+	if err != nil {
+		return "", false, err
+	}
+	if code != 0 {
+		return "", false, nil
+	}
+	out, err := run(repo, "cat-file", "blob", rev+":"+path)
+	return out, true, err
+}
+
 func CommitAll(dir, message, name, email string) (string, error) {
 	status, err := run(dir, "status", "--porcelain", "--untracked-files=all")
 	if err != nil {