A family

The "manual" mode structural descriptions are write in a new files to separate things. But Rougail will concatenate variables and families.

We create a family, which will contain other variables.

This family has:

- a description
- a type

As there is no variable inside this family, the type is mandatory. Without it, Rougail will create a variable.

In fact, this family will be deleted by Rougail too because it is empty.
