Missing void type in LuaPlusCD.h

Hello,
You rewrote your generic type system in 4de30704ee1fe012f7344a517f4c7c699950b0b0 and forgot void type for Type struct. This led to error C2039 ('Get': is not a member of 'LPCD::Type<RT>') in VS2015 when I tried to use LuaPlus::LuaFunction<void> which was hard to understand.