new: added environment.yml to lock down env
new: added environment.yml to lock down env

- Used Anaconda to create a reproducable environment. Anaconda can be
  installed from https://www.continuum.io/downloads. Anaconda is a
  product of Continuum Analytics.
- use `conda env create -f environment.yml` to replicate the env
- use `source activate ladder` to enable the new environment

arasmus/ladder,CuriousAI/ladder