[cmp] Removed the choice vectors.

We agreed that the randomization should happen before every instruction
replaced insted of using always the same alternatie for every invocation
of the function.

For this reason we don't need any more a choice vector but we just need
to call the randmize function with the right parameter.
[cmp] Added the structure explanation.

The second section of the readme gives an overview of the project
organization and a pointer to all the pieces.