Add initial GitHub CI

[aidanheerdegen]

Closes #286

[coveralls]

Coverage increased (+0.08%) to 41.349% when pulling 712be97 on issue-286 into 4dc4a2b on master.

[aidanheerdegen]

@marshallward I can't remember how the RTD are deployed. Does the step for building the docs need to be taken out of the python version matrix and run separately?

[marshallward]

I'm not sure it is ever updated, perhaps it was always manual. I can't see anything configured. Perhaps it would be a good idea to incorporate it.

[aidanheerdegen]

Ok, do RTD automation in another Issue/PR.