Reformat requirements a bit.

requirements.txt

@@ -3,11 +3,8 @@ colour-runner==0.0.4
 coverage==4.0.0
 dj-database-url==0.3
 django==1.8.5
-django-pgcrypto-fields==1.0.0
-djangorestframework==3.2.4
 factory_boy==2.5.2
 flake8-import-order==0.5.1
 incuna-test-utils==6.3.1
 psycopg2==2.6.1
-simplejson==3.8.0
-wheel==0.24.0
+wheel==0.24.0

setup.cfg

@@ -5,6 +5,3 @@ exclude = *migrations*
 statistics = true
 application-import-names = model_logging
 import-order-style = google
-
-[wheel]
-universal = 1

setup.py

@@ -4,6 +4,15 @@
 version = '0.1.0'
 
 
+extras_require={
+    'model_logging': [
+        'django-pgcrypto-fields>=1.0.0,<2.0.0',
+        'simplejson>=3.8.0,<4.0.0',
+        'djangorestframework>=3.2.4,<4.0.0',
+    ]
+}
+
+
 setup(
     name='django-model-logging',
     packages=find_packages(),
@@ -15,7 +24,7 @@
     author_email='[email protected]',
     url='https://github.com/incuna/django-model-logging/',
     install_requires=[],
-    extras_require={},
+    extras_require=extras_require,
     zip_safe=False,
     license='BSD',
     classifiers=[
@@ -24,7 +33,9 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Natural Language :: English',
+        'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3 :: Only',
         'Topic :: Software Development :: Testing',
     ],
 )