add real-time safe Inverse Dynamics library+test+utils

an example for the example browser will follow.
thanks to Thomas Buschmann

Extras/InverseDynamics/DillCreator.hpp

@@ -0,0 +1,47 @@
+#ifndef DILLCREATOR_HPP_
+#define DILLCREATOR_HPP_
+
+#include "MultiBodyTreeCreator.hpp"
+
+namespace btInverseDynamics {
+
+
+/// Creator class for building a "Dill" system as intruduced as benchmark example in
+/// Featherstone (1999), "A Divide-and-Conquer Articulated-Body Algorithm for Parallel O(log(n))
+/// Calculation of Rigid-Body Dynamics. Part 2: Trees, Loops, and Accuracy.",  The International
+/// Journal of Robotics Research 18 (9): 876–892. doi : 10.1177 / 02783649922066628.
+///
+/// This is a self-similar branched tree, somewhat resembling a dill plant
+class DillCreator : public MultiBodyTreeCreator {
+public:
+    /// ctor
+    /// @param levels the number of dill levels
+    DillCreator(int levels);
+    /// dtor
+    ~DillCreator();
+    ///\copydoc MultiBodyTreeCreator::getNumBodies
+    int getNumBodies(int* num_bodies) const;
+    ///\copydoc MultiBodyTreeCreator::getBody
+    int getBody(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:
+    /// recursively generate dill bodies.
+    /// TODO better documentation
+    int recurseDill(const int levels, const int parent, const idScalar d_DH_in,
+                    const idScalar a_DH_in, const idScalar alpha_DH_in);
+    int m_level;
+    int m_num_bodies;
+    std::vector<int> m_parent;
+    std::vector<vec3> m_parent_r_parent_body_ref;
+    std::vector<mat33> m_body_T_parent_ref;
+    std::vector<vec3> m_body_axis_of_motion;
+    std::vector<idScalar> m_mass;
+    std::vector<vec3> m_body_r_body_com;
+    std::vector<mat33> m_body_I_body;
+    int m_current_body;
+};
+}
+#endif