Function function1 

pub fn function1<F, A0, R>(f: F) -> Function1<F, A0, R>
where
    F: Fn(A0) -> R + 'static,
    A0: LuaReadArg + 'static,
    R: PushToLua + 'static,

Wrap a Rust closure so it can be stored as a Lua global via Lua::set.