Import all module packages in __init__.py

I was very confused that `dir(streamparse)` and tab-completion didn't work in IPython after I did `import streamparse`. This fixes that problem.
Tweaks to make sure contextlib2 gets installed for 2.7 on Travis.
Merge pull request #35 from dan-blanchard/patch-1

Import all module packages in __init__.py -- also updates Travis build for 2.x / 3.x support.