Add version classifiers

Author: hugovk

setup.py

@@ -174,7 +174,14 @@
         'Operating System :: Microsoft :: Windows',
         'Operating System :: POSIX :: Linux',
         'Programming Language :: Python',
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 2.6',
+        'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.3',
+        'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
         'Topic :: Security',
         'Topic :: Internet',
         'Topic :: Scientific/Engineering',