Python 3.x compatibility

[michaelsilver]

Looks like the futurize script, available after running pip install future, might be a good place to start. Here's a good reference: http://python-future.org/compatible_idioms.html

You can set up travis to test across all python versions like this:

diff --git a/.travis.yml b/.travis.yml
index 17306a6..116b0a4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,13 @@
 language: python
 python:
+  - "2.6"
   - "2.7"
+  - "3.2"
+  - "3.3"
+  - "3.4"
+  - "3.5"
+  - "3.5-dev" # 3.5 development branch
+  - "nightly" # currently points to 3.6-dev
 install:
   - pip install codecov pep8
   - python setup.py install