Automatically find valid python packages for installation (#921)

Fixes #920
diff --git a/setup.py b/setup.py
index fe2a046..70e57da 100644
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,7 @@
 import sys
 import unittest
 
-from setuptools import setup, Command
+from setuptools import find_packages, setup, Command
 
 import yapf
 
@@ -49,7 +49,7 @@
       author='Google Inc.',
       maintainer='Bill Wendling',
       maintainer_email='[email protected]',
-      packages=['yapf', 'yapf.yapflib', 'yapftests'],
+      packages=find_packages('.'),
       classifiers=[
           'Development Status :: 4 - Beta',
           'Environment :: Console',