Fixes my install problem.

To reproduce:

git clone <this repo>

virtualenv env
source env/bin/activate
python setup.py install
cd ~/ (or anywhere the module won't be on the current path)

python

  > import armstrong.esi

  Will fail, as the __init__.py isn't installed.

  I think you all know this namespace packaging stuff better than I do,
  so please let me know if there's a better solution here!