Memory leak when the signal is destroyed before the fteng::connection is destroyed

[Philippe91]

If the signal is destroyed after the connected functor, then there is a leak.

Example:

	std::function<void()> stdFunction = [] {};

	auto* testSignal = new fteng::signal<void()>;
	fteng::connection connection = testSignal->connect(std::move(stdFunction));

	delete testSignal;

The leaked object is 'f_type' allocated from the line:

new (&call.object) unique{ new f_type(std::move(functor)) };

inside connect(F&& functor)

[mikezackles]

Does #22 fix your problem?