Document interface

[zsunberg]

The interface should be documented very clearly. Currently, there is a list of functions in the readme, but that is not complete (it doesn't include stage for instance).

Probably the best way to do this is with Documenter.jl

[Omastto1]

I completed the initial version of the Documentation using Documenter.jl in my fork.
I had a couple of errors with generating and building that, but for now, it works. I will try to look at the rest tomorrow.

For now, I created my own GitHub Page. I suppose that we will have to change the source codes when merging?

[zsunberg]

If you set it up right, it should automatically create a page at https://juliapomdp.github.io/FiniteHorizonPOMDPs.jl/stable/

[Omastto1]

Currently, the documentation is set up at https://omastto1.github.io/FiniteHorizonPOMDPs.jl/stable.