Functions for implementors

The signatures and documentation of these functions are provided by the files `ap_generic.h', `ap_linearize.h' and `ap_reducedproduct.h'.

These functions are dedicated to implementors of underlying libraries. They offer generic default implementations for some of the operations required by the APRON API, when there is no more specific and efficient implementation for the domain being implemented.

To use one of these, the function allocating manager, which is specific to the domain, should put the corresponding pointer in the virtual table to such a generic implementation.

They manipulated "unboxed" abstract values, which are native to the underlying library: they are not yet boxed with the manager in the type ap_abstract0_t.