Rewrite maps, tuples, lists as BDDs. Performance improvements.

[gldubc]

Changing the representation of maps, tuples to instead use trees (binary decision diagrams).

As we use more and more the difference operator in the type system (e.g. to compute fun_from_inferred_clauses(args_clauses) for inferred function types from patterns), the "DNF" representation started running into pathological cases and hog out time during emptiness checks, and printing.

The BDD is now used for set operations and subtyping, and translated (using previous logic and simplications) to DNF for printing and type operations like map fetch.

The BDD representation is common to maps, tuples, lists and functions. Some functions are generic (called bdd_difference, bdd_intersection, ...).

We also changes some algorithms:

• tuple_eliminate_negation was not generating disjoint tuples. It now does, which greatly improves performance and printing quality.
  -tuple_empty? now uses the same logic, this improves performances.
• pivot_overlapping_clauses algorithm was not generating disjoint tuples. It now does.
• The computation of subtyping for functions and function application is too slow for large arrow intersections (>30). This adds a special case apply_disjoint, when the functions are disjoint and non-empty (as produced by fun_from_inferred_clauses, for instance), which is much faster.