Document all supported Python versions as trove classifiers

I frequently use PyPI trove classifiers to check if a 3rd party package
is usable by my projects. Documenting the supported versions makes this
much easier for potential library users.

Author: jdufresne

setup.py

@@ -51,7 +51,15 @@ def get_long_description():
         'Operating System :: OS Independent',
         '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',
+        'Programming Language :: Python :: Implementation :: CPython',
+        'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Software Development :: Libraries :: Python Modules',
     ],
     test_suite='testsuite.test_all.suite',