[Idea] make all in cpp file format

[zabidenhtf]

And also change format in headers (from h to hpp)

[petitlapin]

what would be the benefit :)? I can understand that some people are more used to cpp/hpp but .cc/.h are still valid c++ extensions and I don't see a big benefit to change it (the cost to do it is also low and there is almost no risk) except doing a change for the sake of doing a change and a taste preference