- add tests for basic data structures of the Tallying algorithm
- Fix all tests for norm (finally converging)

Tallying.CS.cup -> union
Tallying.CS.cap -> prod

lessgeneral m1 m2 check if the constraint set m1 is less general of m2

- More api changes

- separate the merge and solve function in the Tallying module

- the bug was introduced in compute_hash a while ago

- type variables are now correctly parsed as patterns
  and not as expressions

- Add a new module Var that contains all the type variables
  related machinery

- Remove old functions and unit tests about BoolVar of only
  variables, since now variables are always stored associated
  with one or more kinds

- revert a few chances I did before in the code
- add new unit tests functions for the Tallying problem

BoolVar.get not is reinstated to return a list of pairs
Add new unit test for Types.witness (WIP)

typesOUnit.cma won't compile for some strange reason

For the moment are identied as `$X and interpreted as atoms

All tests are taken from the poly cduce prototype.
All tests pass.

based on oUnit

this patch probably makes cduce inomcpatible with ocaml 3.07

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