Created by: cmcarthur
This branch:
- adds test support for Python 3.5, 3.6
- removes the now-unsupported Python 2.6
- upgrades openpyxl to 2.2.5, which has no breaking changes from 2.2.0 but includes bugfixes
- fixes a couple errors in the tests (
IOError: file must be opened in binary mode
)