setup.py: Claim compatibility through 3.5

I haven't actually tested all of these, but I doubt I did anything so
magical that support has been dropped in the meantime ;).  It would be
nice to drop the doctests [1], but until then testing Python 3 is
going to be difficult.

[1]: https://github.com/wking/igor/pull/1#issuecomment-190309065

setup.py

@@ -47,6 +47,9 @@ setup(name=package_name,
         'Programming Language :: Python',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3.2',
+        'Programming Language :: Python :: 3.3',
+        'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.5',
         'Topic :: Scientific/Engineering',
         'Topic :: Software Development :: Libraries :: Python Modules',
         ],