Add missing classifiers to setup.py (close snowplow#148)

Author: chuwy

setup.py

@@ -61,10 +61,17 @@
     long_description=open('README.rst').read(),
 
     classifiers=[
-        "Development Status :: 4 - Beta",
+        "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",
-        "Programming Language :: Python"
+        "Programming Language :: Python",
+        "Programming Language :: Python :: 2",
+        "Programming Language :: Python :: 2.7",
+        "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.3",
+        "Programming Language :: Python :: 3.4",
+        "Programming Language :: Python :: 3.5",
+        "Operating System :: OS Independent",
     ],
 
     install_requires = [