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

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

src/BulletInverseDynamics/premake4.lua

@@ -0,0 +1,12 @@
+	project "BulletInverseDynamics"
+
+	kind "StaticLib"
+	includedirs {
+		"..",
+	}
+	files {
+		"IDMath.cpp",
+		"MultiBodyTree.cpp",
+		"details/MultiBodyTreeInitCache.cpp",
+		"details/MultiBodyTreeImpl.cpp",
+	}