Merge branch '171-refactoring-move-distance_map-generation-from-obs_builder-to-railenv' into 'master'

Refactoring: move distance_map from ObservationBuilder to RailEnv

Closes #171

See merge request flatland/flatland!187

Merge branch 'master' of gitlab.aicrowd.com:flatland/flatland into 171-refactoring-move-distance_map-generation-from-obs_builder-to-railenv

# Conflicts:
#	examples/custom_observation_example.py

Resolve "benchmarks_and_profiling: The script exceeded the maximum execution time set for the job"

Closes #175

See merge request flatland/flatland!189

Refactoring: distance_map is initialized in constructor, so checks like hasattr(self, 'distance_map') are unnecessary

Refactoring: delete new_position from TreeObsForRailEnv and use flatland.core.grid.grid4utils.get_new_position instead

Update flatland_2.0.md for a minor typo

See merge request flatland/flatland!188

Merge branch 'master' of gitlab.aicrowd.com:flatland/flatland into 175-no-sleep-when-running-examples-as-benchmark-or-profiling

Resolve "Bug: sparse_rail_generator might not generate an agent/target pair : Results in number of agents == 0."

Closes #176

See merge request flatland/flatland!185

#160 predictor documentation

Closes #160

See merge request flatland/flatland!184

#80 specifications as markdown moved from wiki

Closes #161, #159, and #79

See merge request flatland/flatland!182

#79 bugfix sphinx generated documentation #161 observation documentation  #159 documentation about new INFO

Update flatland_2.0.md

See merge request flatland/flatland!181

#167 bugfix action_on_cellexit

Closes #167, #162, and #164

See merge request flatland/flatland!179