def commit_data(sha)
      sha = sha.to_s
      cdata = command_lines('cat-file', ['commit', sha])
      process_commit_data(cdata, sha, 0)
    end
def commit_data(sha)
      sha = sha.to_s
      cdata = command_lines('cat-file', ['commit', sha])
      process_commit_data(cdata, sha, 0)
    end
returns useful array of raw commit object data