setup.py: Switch to setuptools

Apparently we can't declare dependencies without it.

Author: bgilbert

.gitignore

@@ -1,3 +1,4 @@
 /build
 /dist
 /MANIFEST
+/*.egg-info

README.txt

@@ -4,6 +4,8 @@ OpenSlide Python requires:
 * OpenSlide >= 3.4.0
 * Python Imaging Library or Pillow
 
+Installation requires setuptools.
+
 To install:
 
     python setup.py install

setup.py

@@ -1,5 +1,5 @@
-from distutils.core import setup
 import os
+from setuptools import setup
 
 # Load version string
 _verfile = os.path.join(os.path.dirname(__file__), 'openslide', '_version.py')
@@ -18,4 +18,8 @@
     license='GNU Lesser General Public License, version 2.1',
     keywords='openslide whole-slide image library',
     url='http://openslide.org/',
+    install_requires=[
+        'Pillow',
+    ],
+    zip_safe=True,
 )