Add PyPI publishing support

Taken directly from the known working azavea/python-omgeo#33

.travis.yml

@@ -36,5 +36,15 @@ install:
 script:
   - coverage run --source=django_tinsel test_app/manage.py test django_tinsel_tests
 
+deploy:
+  provider: pypi
+  user: azavea
+  password:
+    secure: Wc/aboeIntZeqgCSIOrd/66vceukY/KmdSLwcLB9gn7kRWRqOM+HiEX9+lJe4IKtMisz3zgRqZNAFJU/UUBBwuclHpbtQtV0FCQOFXEwUHQfouzAvVu/3C4fBgQeoet5KrJFo7OVUmYwyWPm8vJzWIraQWVfsR9Gv/AQBQdfuec=
+  on:
+    tags: true
+    distributions: sdist bdist_wheel
+    repo: azavea/django-tinsel
+
 after_success:
   - coveralls --verbose