[InverseDynamics] Support for Jacobians & derivatives

This change adds support for calculating Jacobians and
dot(Jacobian)*u terms, along with the required support for
the 3xN matrices in the standalone math library.
It also adds functions to compute kinematics only (position, velocity, accel).
To facilitate tests, the Cl also adds a RandomTreeCreator to create
randomized multibody trees.
Thanks to Thomas Buschmann for this contribution!

Extras/InverseDynamics/CloneTreeCreator.hpp

@@ -0,0 +1,27 @@
+#ifndef CLONETREE_CREATOR_HPP_
+#define CLONETREE_CREATOR_HPP_
+
+#include "BulletInverseDynamics/IDConfig.hpp"
+#include "MultiBodyTreeCreator.hpp"
+
+namespace btInverseDynamics {
+/// Generate an identical multibody tree from a reference system.
+class CloneTreeCreator : public MultiBodyTreeCreator {
+public:
+    /// ctor
+    /// @param reference the MultiBodyTree to clone
+    CloneTreeCreator(const MultiBodyTree*reference);
+    ~CloneTreeCreator();
+    ///\copydoc MultiBodyTreeCreator::getNumBodies
+    int getNumBodies(int* num_bodies) const;
+    ///\copydoc MultiBodyTreeCreator::getBody
+    int getBody(const int body_index, int* parent_index, JointType* joint_type,
+                vec3* parent_r_parent_body_ref, mat33* body_T_parent_ref, vec3* body_axis_of_motion,
+                idScalar* mass, vec3* body_r_body_com, mat33* body_I_body, int* user_int,
+                void** user_ptr) const;
+
+private:
+    const MultiBodyTree *m_reference;
+};
+}
+#endif  // CLONETREE_CREATOR_HPP_