Adds a damped least squares (DLS) IK solver that is more robust than Gauss-Newton in singular configurations, with a tunable damping parameter for improved numerical stability, also known as the Levenberg-Marquardt method.

Adds the HField class and SceneModel members: get_hfield_index(name), get_hfield(arg), and the num_hfields property, for accessing and managing height field objects by name.

MJCF now allows configuring the mocap attribute on a link; mocap objects are unaffected by forces but can apply forces to other bodies. The new Mocap class lets you set their pose directly through the API.