Test against Python 3.4 and multiple Twisted versions

This commit adds tox to be able to test against different dependencies
locally. We agreed that Python 3.4 should be supported across all Channels
projects, so it is also added with this commit.

Furthermore, I think it makes sense to support a broad range of Twisted
releases, as users of daphne are not unlikely to have other Twisted code
running. It's not feasible to test against all releases since 16.0, and
it would require constant maintenance to add new releases as they come
out. So I opted to keep things simple for now, and only test against the
oldest supported and the current Twisted release.

I did consider @jpic's great idea from
https://github.com/django/daphne/pull/19 to just use tox to avoid having
to duplicate the dependency matrix. But it does lead to slower test runs
as it bypasses Travis' caching, and is slightly more verbose.

.gitignore

@@ -3,3 +3,4 @@
 __pycache__
 dist/
 build/
+/.tox

.travis.yml

@@ -1,9 +1,16 @@
 sudo: false
+
 language: python
+
 python:
   - "2.7"
+  - "3.4"
   - "3.5"
-install:
-  - if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then pip install unittest2; fi
-  - pip install asgiref twisted autobahn
-script: if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then python -m unittest2; else python -m unittest; fi
+
+env:
+  - TWISTED_RELEASE="twisted"
+  - TWISTED_RELEASE="twisted==16.0.0"
+
+install: pip install $TWISTED_RELEASE -e .
+
+script: python -m unittest discover

setup.py

@@ -40,6 +40,7 @@ setup(
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Topic :: Internet :: WWW/HTTP',
     ],

tox.ini

@@ -0,0 +1,8 @@
+# We test against the oldest supported Twisted release, and the current release.
+[tox]
+envlist = py{27,34,35}-twisted-{old,new}
+
+[testenv]
+deps =
+    twisted-old: twisted==16.0.0
+commands = python -m unittest discover