Merge branch 'master' of gitlab.aicrowd.com:flatland/flatland into 169-Enhance_sparse_rail_generator

Resolve "Refactoring: unification of apidoc of parameter / return"

Closes #174, #33, #149, and #31

See merge request flatland/flatland!192

#178 bugfix initial malfunction

Closes #178

See merge request flatland/flatland!191

Merge branch 'master' of ssh://gitlab.aicrowd.com/flatland/flatland into 169-Enhance_sparse_rail_generator

Resolve "SparseRailGenerator : Agent placement (invalid direction)"

Closes #182

See merge request flatland/flatland!193

Merge branch 'master' of ssh://gitlab.aicrowd.com/flatland/flatland into 169-Enhance_sparse_rail_generator