fromHeathrowToLondon: data type definitions
fromHeathrowToLondon: Heathrow to London represented as a RoadSystem
fromHeathrowToLondon: more data type definitions
fromHeathrowToLondon: Heathrow to London solution represented as a Path
fromHeathrowToLondon: roadStep function type
fromHeathrowToLondon: roadStep implementation
fromHeathrowToLondon: optimalPath implementation
fromHeathrowToLondon: timeFor helper and some refactor
fromHeathrowToLondon: groupsOf implementation
fromHeathrowToLondon: main implementation