utils

"Array<another_data_type>" is actually (CastArray<another_data_type>).  This is
in fact just a view which allow to access/modify original array's data
reinterpreting them to another type.

The only constrain w.r. to the type is that one must have
sizeof(data_type)*Array::size() == sizeof(other_data_type)*CastArray::size().

CastArray can be built thanks to the helper static function
cast_array_to<other_data_type>::from(given_array).

Usage: for instance, one writes:

Array<double> x(3); x[0]=1;x[1]=2;x[2]=3;
CastArray y = cast_array_to<int>::from(x);        // ok! y values can change
CastArray z = cast_array_to<const int>::from(x);  // ok! z values cannot change

Array<const double> cx = x;
CastArray cy = cast_array_to<int>::from(cx);      // invalid! cannot remove const
CastArray cz = cast_array_to<const int>::from(cx);// ok!

CastArray t = cast_array_to<TinyVector<4,int>>::from(x); // ok!

In last example, execution will fail (sizes are incompatible), but would success
if the size of x was a multiple of 2.

It is unclear if one should impose sizeof(other_data_type) <= sizeof(data_type)