removed JsonToWorldConverter in favor of dedicated method in World
removed JsonToMapConverter in favor of dedicated method in Map
removed Vector2ToJsonConverter in favor of a dedicated method in Vector2
removed ClosedShapeToJsonConverter in favor of a dedicated method in
ClocsedShape
removed InternalSpringToJsonConverter in favor of dedicated method in
InternalSpring
added SpringPhysics to handle Springs inside a Body
removed BodyToJsonConverter in favor of a dedicated method in Body and
its subclasses
removed WorldToJsonConverter in favor of a dedicated method in World
removed MapToJsonConverter in favor of a dedicated method in Map
introduce SpringPhysics as a layer of indirection for springs
added useSprings and usePressure flags in BodyDefinition
moved toJson to PressurePhysics
adjusted PressureBodies to be SpringBodies as well
added dedicated method to create physics components for Bodies
handle toJson in PressurePhysics via out parameter
moved methods to handle SpringPhysics from SpringBody to Body
moved handling of PressurePhysics from PressureBody to Body
replace explicit class reference with type strings
removed references to SpringBody and PressureBody
removed PressureBody and SpringBody