Callbacks for interval change and FRC request

[Heiko-L]

Instead of polling for FRC request there is now an option to register a callback function which is called on request.
Furthermore an option for a callback function on interval change is given.

[qfisch]

Hello @Heiko-L
Thank you for your contribution.
Could you make 2 commits out of it in order to clearly detail changes ?
Cheers
Q

[Heiko-L]

Now I reconsidered a bit and think that I keep my hands off the constructor and add callback functionality externally to keep compatibility.
At the same time I also plan to add a lot new characteristics- should there be a commit for every characteristic?

[qfisch]

Your new approach would indeed be better IMO.
Implementing a new DataProvider that implements src/IProviderCallbacks.h but relies on call forwarding is also an option...

Concerning the "paperwork":
I would even make 2 PRs in this case.
One for the callbacks, and one for the characteristics (with detailed commits)
Thanks for your contribution

Q.

[Heiko-L]

I added SCDDataProvider (derived from DataProvider) and SCD4xDataProvider (derived from SCDDataProvider).
Therefore I had to add both as friends of DataProvider. I also had to separate the setup of the BLE services in DataProvider to extend them in the derived classes.
In IBLELibraryWrapper I added a method to register callbacks (which are stored in a std::map in struct WrapperPrivateData) and added 7 new characteristics. I also changed WrapperPrivateData::onWrite to call the registered callbacks.