Add missing trove classifiers to document Python support

Helps library consumers know, at a glance, if the library is suitable
for their project.

Python versions were determined by Travis configuration.

Alphabetized classifiers.

Author: jdufresne

setup.py

@@ -32,13 +32,19 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
-        'Topic :: Documentation',
-        'Topic :: Software Development :: Documentation',
         'Programming Language :: Python',
+        'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.2',
         '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 :: Documentation',
+        'Topic :: Software Development :: Documentation',
     ],
 )