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

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

src/BulletInverseDynamics/IDConfig.hpp

@@ -0,0 +1,40 @@
+///@file Configuration for Inverse Dynamics Library,
+///      such as choice of linear algebra library and underlying scalar type
+#ifndef IDCONFIG_HPP_
+#define IDCONFIG_HPP_
+// If we have a custom configuration, compile without using other parts of bullet.
+#ifdef BT_CUSTOM_INVERSE_DYNAMICS_CONFIG_H
+#define BT_ID_WO_BULLET
+#endif
+// error messages
+#include "IDErrorMessages.hpp"
+
+#ifdef BT_CUSTOM_INVERSE_DYNAMICS_CONFIG_H
+#define INVDYN_INCLUDE_HELPER_2(x) #x
+#define INVDYN_INCLUDE_HELPER(x) INVDYN_INCLUDE_HELPER_2(x)
+#include INVDYN_INCLUDE_HELPER(BT_CUSTOM_INVERSE_DYNAMICS_CONFIG_H)
+#else
+// Use default configuration with bullet's types
+// Use the same scalar type as rest of bullet library
+#include "LinearMath/btScalar.h"
+typedef btScalar idScalar;
+// use bullet types for arrays and array indices
+#include "Bullet3Common/b3AlignedObjectArray.h"
+// this is to make it work with C++2003, otherwise we could do this:
+// template <typename T>
+// using idArray = b3AlignedObjectArray<T>;
+template <typename T>
+struct idArray {
+    typedef b3AlignedObjectArray<T> type;
+};
+typedef int idArrayIdx;
+#define ID_DECLARE_ALIGNED_ALLOCATOR B3_DECLARE_ALIGNED_ALLOCATOR
+
+// use bullet's allocator functions
+#define idMalloc btAllocFunc
+#define idFree btFreeFunc
+
+#define ID_LINEAR_MATH_USE_BULLET
+#include "details/IDLinearMathInterface.hpp"
+#endif
+#endif