Add support for use move-only type as parameter in signal which only has one slot

[xyz1001]

Could you please add support for this code?

#include <iostream>

#include <sigslot/signal.hpp>

class Foo {
public:
    Foo() = default;
    ~Foo() = default;

    Foo(const Foo &) = delete;
    Foo &operator=(const Foo &) = delete;

    Foo(Foo &&) = default;
    Foo &operator=(Foo &&) = default;

public:
    void Test() {
        SigTest(std::make_unique<int>(3));
    }

public:
    sigslot::signal<std::unique_ptr<int> &&> SigTest;
};

class Bar {
public:
    Bar() = default;
    ~Bar() = default;

    Bar(const Bar &) = delete;
    Bar &operator=(const Bar &) = delete;

    Bar(Bar &&) = default;
    Bar &operator=(Bar &&) = default;

public:
    void OnTest(std::unique_ptr<int> arg) {
        std::cout << "arg: " << *arg << std::endl;
    }
};

int main() {
    Foo foo;
    Bar bar1;
    Bar bar2;
    foo.SigTest.connect(&Bar::OnTest, &bar1);
    // foo.SigTest.connect(&Bar::OnTest, &bar2); // should be compile time error or runtime error
    foo.Test();
    return 0;
}

Currently I need use std::shared_ptr as parameter, which will cause it is hard to manage lifetime.

Maybe a new signal type which only take one slot is possible way to implement it.

[Pierre-Antoine Lacaze]

Duplicate of #18