This make a better distinction between `stable` software and software
deployed in production.

We define 3 branches:
- `dev`: new developped features are integrated here, this is the
  default branch
- `testing`: is a fork of `dev` when we want to prepare the next
  release, this is the branch from where release bugfixes are derived
  and merged back
- `stable`: is where the `testing` branch is merged to produce a new
  release