docs: update for Documenter 1.x, surface missing docstrings, add POMDPs.jl page#60

jamgochiana wants to merge 4 commits into

arec/pomdps-interfacesisl/GaussianFilters.jl:arec/pomdps-interfacefrom

arec/docs-build-fixsisl/GaussianFilters.jl:arec/docs-build-fixCopy head branch name to clipboard