add LG_TypeCheck macro
add LuaGlue::getGlobal<Type> method to fetch globals.
add LuaGlueClass<Class>::getProperty and LuaGlueClass<Class>::setProperty methods to allow setting and getting properties from C++
fix some static/const issues
fix an issue with std::string direct properies (needed a LuaGlueDirectProperty specialization)
assert in pushInstance if value is null
add LuaGlue::getClass to get a LuaGlueClass<Class> object
add internal __concat metamethod to all LuaGlueClass's to stringify LuaGlueClass objects to 'ClassName(ptr)'