Set metadata to Py3 only + Remove Universal Wheel (#50)

* Set metadata to Py3 only + Remove Universal Wheel

- I see not inclusion of deps + support in code for Python 2
- Lets remove making a universal wheel then + flag in setup.py that this code is Python 3 only

* Add python_requires + use same quotation marks everywhere

Author: cooperlees

setup.cfg

@@ -41,12 +41,14 @@
         "Intended Audience :: Developers",
         "Operating System :: OS Independent",
         "Programming Language :: Python",
-        "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3 :: Only",
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
+        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: Implementation :: CPython",
     ],
     install_requires=install_requires,
+    python_requires="~=3.4",
 
     test_suite="test_elasticsearch_async.run_tests.run_all",
     tests_require=tests_require,