It computes the euclidean distance and finish the simulation if the
distance is above the tolerance epsilon.
I ha to change some function signature of types in core/model.jl but it
was minor changes.
I add a new test + change some others related to automata.
A minor rewriting core/model for better readability

models. It's a better semantic and improve performance as well as
readability of the code. All the tests passes (except the remark in the
last commit).

R1,R2,R3.