Refactor Int ?

[thomas-lamiaux]

Currently in Int there is a bunch of properties like +Comm that maybe should be hidden. Indeed they are often in double with opening a RingStr

[thomas-lamiaux]

We talked about it, the idea would be to

• Put those lemma in named module so that people have to open it to acces it.

• Add comment on top of the concern files saying not to use them but to use the following instances [...] instead . For instance the CommRing for Int

  • Add a more general comment in contributing, possibly completing the current one on modules.

  The concerned files would be at least Int and Nat