make LuaTable, LuaCoroutine, LuaFunction and LuaUserdata constructible

[davidsiaw]

Theres no way to new these things, and it might be irritating to people.

[davidsiaw]

Easy just make them constructors that take the lua object

[davidsiaw]

c++0x issue. Constructors cannot be delegated yet until c++11! Well, I guess this means a little bit of duplicated code.