Provide a solution for using class member functions as callback

[AlirezaSalehy]

Hi, There!

Thanks again for your useful library and the effort made. Recently, I have been struggling to find a way to use member functions as PropertyChanged callback but as you possibly know it's not possible in this version of the library. But I request to change the callback definitions that is originally like this:

void (*callback_)(ThingPropertyValue) = nullptr)

to this:

std::function<void(ThingPropertyValue)> callback_

According to my investigations, the neatest way to make member functions used as callback is by using functional and std::function concept; this way we can easily pass lambda functions as callbacks.

So I was wondering if there is a technical issue that impedes the usage of functional. And if there's no then I'd be so grateful to be able to contribute to this issue.

Thanks in advance!