Simplify version mentioning in README, classifiers

Remove Python version mentionings, as they are beholden to Django's
constraints.

See also:

- #305

README.rst

@@ -14,21 +14,19 @@ django-model-utils
 
 Django model mixins and utilities.
 
-``django-model-utils`` supports `Django`_ 1.8 through 1.10 (latest bugfix
-release in each series only) on Python 2.7, 3.3 (Django 1.8 only), 3.4 and 3.5.
+``django-model-utils`` supports `Django`_ 1.8 to 2.0.
 
 .. _Django: http://www.djangoproject.com/
 
 This app is available on `PyPI`_.
 
 .. _PyPI: https://pypi.python.org/pypi/django-model-utils/
 
-
 Getting Help
 ============
 
-Documentation for django-model-utils is available at https://django-model-utils.readthedocs.io/
-
+Documentation for django-model-utils is available
+https://django-model-utils.readthedocs.io/
 
 Contributing
 ============

setup.py

@@ -46,7 +46,11 @@ def get_version(root_path):
         'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
         'Framework :: Django',
+        'Framework :: Django :: 1.8',
+        'Framework :: Django :: 1.9',
+        'Framework :: Django :: 1.10',
         'Framework :: Django :: 1.11',
         'Framework :: Django :: 2.0',
     ],