add Lua and basic Lua->C/C++ integration test, in preparation for Bullet demos setup using Lua scripts.

btgui/lua-5.2.3/src/lua.hpp

@@ -0,0 +1,9 @@
+// lua.hpp
+// Lua header files for C++
+// <<extern "C">> not supplied automatically because Lua also compiles as C++
+
+extern "C" {
+#include "lua.h"
+#include "lualib.h"
+#include "lauxlib.h"
+}