Globsim

This is the release of GlobSim to go with the initial submission of the manuscript to Geoscientific Model Development (GMD), the discussion stage (GMDD)

Testing that everything works with docker and readthedocs

Setting a release here because it marks a milestone of:
- all 3 datasources working with python 3 and backwards compatible with 2 (although not rigorously tested)
- last commit before branching off master to have a "working" branch which should allow for <master> to have strictly working releases
- approximate transition point with regards to personnel: Xiaojing has finished, Bin and Nick are just starting