jointWith 
  inline fun <J : JointDef> Body.jointWith(body: Body, jointDefinition: J, init: J.() -> Unit = {}): Joint
Allows to create a Joint with custom JointDef instance. this Body will be set as the JointDef.bodyA.
Return
a fully constructed Joint based on the customized jointDefinition.
Parameters
body
will be set as the JointDef.bodyB.
jointDefinition 
can be customized with init block.
init
inlined. JointDef.bodyA, JointDef.bodyB and JointDef.type must not be changed. Invoked after joint definition default values are preset.