From the ast point of view this gives cleaner data type description.
Nodes used to describe type names are now explicitly described as
type names. Previously,

- the data type could be marked as the described type. Now it is
referred as the `typename` of the type. For instance the `R^2`
type descriptor node was given `R^2` as a data type. Now it is given
the `typename(R^2)`: it is a typename which refers to `R^2`.
- In some other cases, it could have been just `typename` which forced
to re-parse entries (which is never good).

Also `affectations` types is fixed: it is now given the `void` type
instead of the type of the affected data.

Functions input and output spaces types should now be correctly
defined: some more tests are however required.

The case of compound types is however not that clear since the data
type of the type `R*R*R^2` is just defined as `typename(list)`. This
may be improved (in order to help checking of function definition/use.

An initialization issue related to tuples of R^1 was fixed on the way
and some error messages improved.

This is related to issue #21