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

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

src/BulletInverseDynamics/IDConfigEigen.hpp

@@ -0,0 +1,43 @@
+///@file Configuration for Inverse Dynamics Library with Eigen
+#ifndef INVDYNCONFIG_EIGEN_HPP_
+#define INVDYNCONFIG_EIGEN_HPP_
+#ifdef BT_USE_DOUBLE_PRECISION
+// choose double/single precision version
+typedef double idScalar;
+#else
+typedef float idScalar;
+#endif
+
+// use std::vector for arrays
+#include <vector>
+// this is to make it work with C++2003, otherwise we could do this
+// template <typename T>
+// using idArray = std::vector<T>;
+template <typename T>
+struct idArray {
+    typedef std::vector<T> type;
+};
+typedef std::vector<int>::size_type idArrayIdx;
+// default to standard malloc/free
+#include <cstdlib>
+#define idMalloc ::malloc
+
+#define idFree ::free
+// currently not aligned at all...
+#define ID_DECLARE_ALIGNED_ALLOCATOR()                                                             \
+    inline void* operator new(std::size_t sizeInBytes) { return idMalloc(sizeInBytes); }           \
+    inline void operator delete(void* ptr) { idFree(ptr); }                                        \
+    inline void* operator new(std::size_t, void* ptr) { return ptr; }                              \
+    inline void operator delete(void*, void*) {}                                                   \
+    inline void* operator new[](std::size_t sizeInBytes) { return idMalloc(sizeInBytes); }         \
+    inline void operator delete[](void* ptr) { idFree(ptr); }                                      \
+    inline void* operator new[](std::size_t, void* ptr) { return ptr; }                            \
+    inline void operator delete[](void*, void*) {}
+
+// Note on interfaces:
+// Eigen::Matrix has data(), to get c-array storage
+// HOWEVER: default storage is column-major!
+#define ID_LINEAR_MATH_USE_EIGEN
+#include "Eigen/Eigen"
+#include "details/IDEigenInterface.hpp"
+#endif