Switch from distutils to setuptools

This allows wheels to be build for this package.

setup.py

diff --git a/setup.py b/setup.py
index 77c5f8f..b6aa871 100644
--- a/setup.py
+++ b/setup.py
@@ -14,11 +14,13 @@
 #
 """Simple distutils setup for the pure Python portpicker."""
 
-import distutils.core
 import sys
 import textwrap
 
 
+import setuptools
+
+
 def main():
     requires = []
     scripts = []
@@ -31,7 +33,7 @@
         # The example portserver implementation requires Python 3 and asyncio.
         scripts.append('src/portserver.py')
 
-    distutils.core.setup(
+    setuptools.setup(
         name='portpicker',
         version='1.2.0',
         description='A library to choose unique available network ports.',