Stop Decoding Values

Currently http-parser converts certain values to `str` on Python3 instead of leaving them as bytes. This allows treating things which are pure ASCII as strings, however in order to do anything more complex than that is requires an encoding dance to go back to bytes by encoding with latin1 again, and then potentially decoding them again with a different encoding. It would be nice if http-parser at least allowed disabling the decoding if not just stopped doing it altogether.