add classifiers to setup.py

Author: pipermerriam

setup.py

@@ -40,4 +40,13 @@
         "https://github.com/ulope/secp256k1-py/archive/master.zip#egg=secp256k1-0.11.1"
     ],
     version=version,
+    classifiers=[
+        'Intended Audience :: Developers',
+        'Natural Language :: English',
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.3',
+        'Programming Language :: Python :: 3.4',
+    ],
 )