Issue: mbed 5 and deprecation warnings

Hi there. Apologies in advance if this has already been discussed/resolved somewhere and I am unaware of it.

I am making use of your *Really* Useful code with mbed 5 (on an STM MCU). However, mbed 5 has changed the function pointer/callback scheme a few times and so I get deprecation warnings when compiling, which I would like to clean up. I know how to modify the code to work without warnings on mbed 5 (files can be found here: https://1drv.ms/f/s!AqUHa_qo4gdB7G7j9NCUJizHY51w, if you're interested) but forking it for this reason would be a shame, since the code works perfectly well as it is. That, and I can only test the changes on my STM platform.

Question is, what would you recommend I do? I could propose some changes, under an `#if MBED_MAJOR_VERSION >= 5` switch, that have been tested on my STM platform, or a fork of the code could be created in github for mbed 5 purposes, or I could fork the code just for my needs, or something else...?

Thanks in advance for your help (and your very useful code).