Continuous Observations

It would be nice to have an offline solver, which can handle continuous observation spaces (or large discrete ones). Hoey & Poupart [1] introduced an extension of point-based methods, which works by partitioning the observation space into a small set of regions, which lead to the same conditional plan.

I might give implementing their method a try at some point, but I am not sure whether this should be implemented as an extension of `PointBasedValueIteration.jl` or as a standalone package.

[1] Hoey, J., & Poupart, P. (2005, July). Solving POMDPs with continuous or large discrete observation spaces. In IJCAI (pp. 1332-1338).