* [core] Make visual and collision models optional.
* [core] Throw exception when trying to alter hardware or controller internals during simulation.
* [core] Mark src-local functions as static.
* [core] Add some missing bad control flow checks.
* [core/python] 'Model' can now be instantiated from Python.
* [core/python] Fix partially broken 'FunctionalController' bindings.
* [core/python] Avoid visitor pattern when irrelevant.

* [core] Print warnings even for release build type.
* [core/python] Expose more methods for 'Model'.
* [core/python] Fix multiple typos.
* [python/simulator] Fix 'robot' and 'robot_state' corrupted if robot is replaced.
* [gym/common|gym/toolbox] Promote generic SE3 math utilities from toolbox to common module.
* [gym/common] Add 'compute_tilt_from_quat', 'swing_from_vector', and 'remove_twist_from_quat'.
* [gym/common] Fix 'refresh_observation' being called before 'initialize_buffers' at simulation start.
* [gym/common] Fix broken mahony filter for 'twist_time_constant != None'.
* [gym/common] Fix support of non-batched mode for generic math.
* [gym/common] Fix 'matrix_to_rpy' to be consistent with 'pin.matrixToRpy'.
* [gym/envs] Fix broken 'Ant' environment.

* [core] Fix broken 'getRigidVelocityFromFlexible'.
* [gym/common] Add 'DeformationEstimator' block.

)