Remove warnings in setup.py and use setuptools instead of distutils

(but since it is not important, use distutils when setuptools is
unavailable)

setup.py

 #!/usr/bin/env python3
-from distutils.core import setup, Extension
+try:
+    from setuptools import setup, Extension
+except ImportError:
+    from distutils.core import setup, Extension
+
 import os, sys
 
 module_poopt = Extension('poezio.poopt',