Add python_requires to help pip

Author: hugovk

setup.py

@@ -16,6 +16,7 @@
     scripts=['bin/jp.py'],
     packages=find_packages(exclude=['tests']),
     license='MIT',
+    python_requires='>=2.6, !=3.0.*, !=3.1.*, !=3.2.*',
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Intended Audience :: Developers',