Use std::function instead of raw function pointers #25

Hey, thanks for the amazing library!
I really want to use this in a modern codebase with lots of classes, but the DataFunction class does not accept a function or data from my class members, as it is typed with a raw function pointer.
I would love to see std::function being used instead on supported platforms (which is most of the modern ones, like RP2040 and ESP32).