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

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

Extras/InverseDynamics/MultiBodyTreeDebugGraph.hpp

@@ -0,0 +1,17 @@
+#ifndef MULTIBODYTREEDEBUGGRAPH_HPP_
+#define MULTIBODYTREEDEBUGGRAPH_HPP_
+#include "BulletInverseDynamics/IDConfig.hpp"
+#include "BulletInverseDynamics/MultiBodyTree.hpp"
+#include "MultiBodyNameMap.hpp"
+
+namespace btInverseDynamics {
+/// generate a dot-file of the multibody tree for generating a graph using graphviz' dot tool
+/// @param tree the multibody tree
+/// @param map to add names of links (if 0x0, no names will be added)
+/// @param filename name for the output file
+/// @return 0 on success, -1 on error
+int writeGraphvizDotFile(const MultiBodyTree* tree, const MultiBodyNameMap* map,
+                         const char* filename);
+}
+
+#endif  // MULTIBODYTREEDEBUGGRAPH_HPP