-convert sensors module into a package
-make JointSensor.__init__ be able to receive a Joint OR a SimulatedJoint, which
wraps a Joint. The idea is to avoid confusing calls such as "x.get_joint().get_joint()"
+-rename package "model" to "core"?
Conventions and consistency:
-rename '_inner_object'/'inner_object' to '_inner_obj'/'inner_obj'
-dBodySetFiniteRotationAxis. is it necessary to set this if dBodySetFiniteRotationMode = true?
-rename package "model" to "core"?
-split 'tests' and what are examples of how to use external libs