Brand new implementation based on functors taking a strategy in input.

Brand new implementation based on functors taking a strategy in input.
Several different strategies have been implemented. Unfortunately many
of them are incomparable and there are critical examples where only some
of them terminate in reasonable time.

Removing the functor/module stuff does not bring any sensible performance
improvement even for simple strategies (where most of the functions are
just identity fuctions that can be inlined when not crossing functor
boundaries).