Enhancement: Debounce input pins

[zpfvo]

Hi,
i'm using this library in one of our products. I just came back from an EMC test and we sometimes had a problem with a toggling pin when our board was exposed to electromagnetic radiation.

We could solve the problem easily by checking if the state of the pin stayed the same for a short period of time.
I implemented this debounce logic in the callback function but i thought if this was a nice feature to be embedded in the library itself.

If you think this might be a nice idea, i will prepare a pull request to add this functionality as soon as i have some time (sry very busy atm). I think it would be nice if one activate debounce separately for the pins and also set different deboucne times.

Greetings!