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

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

Extras/InverseDynamics/IDRandomUtil.hpp

@@ -0,0 +1,34 @@
+#ifndef ID_RANDOM_UTIL_HPP_
+#define ID_RANDOM_UTIL_HPP_
+#include "BulletInverseDynamics/IDConfig.hpp"
+namespace btInverseDynamics {
+/// seed random number generator
+void randomInit();
+/// Generate (not quite) uniformly distributed random integers in [low, high]
+/// Note: this is a low-quality implementation using only rand(), as
+/// C++11 <random> is not supported in bullet.
+/// The results will *not* be perfectly uniform.
+/// \param low is the lower bound (inclusive)
+/// \param high is the lower bound (inclusive)
+/// \return a random number within [\param low, \param high]
+int randomInt(int low, int high);
+/// Generate a (not quite) uniformly distributed random floats in [low, high]
+/// Note: this is a low-quality implementation using only rand(), as
+/// C++11 <random> is not supported in bullet.
+/// The results will *not* be perfectly uniform.
+/// \param low is the lower bound (inclusive)
+/// \param high is the lower bound (inclusive)
+/// \return a random number within [\param low, \param high]
+float randomFloat(float low, float high);
+
+/// generate a random valid mass value
+/// \returns random mass
+float randomMass();
+/// generate a random valid vector of principal moments of inertia
+vec3 randomInertiaPrincipal();
+/// generate a random valid moment of inertia matrix
+mat33 randomInertiaMatrix();
+/// generate a random unit vector
+vec3 randomAxis();
+}
+#endif