Add testing / automation infrastructure

Adds a RoboFile for task orchestration (in this case a fluffed-up Makefile) as well as Codeception for running acceptance tests.

I haven't added the travis badge to the README because I couldn't get travis to work correctly w/ the acceptance testing, dunno why. Here's an example: https://travis-ci.org/ciarand/purplapp/jobs/35793264

A. It's failing and B. it's returning a 0 (success) exit code?

(Closes #30)