Fix of distributed abc smc tests + add of a test.
Preparation for the new feature: add a stop criteria in the simulation.
All tests passed.

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

The solution is to use FunctionWrappers.jl which provides a high
interface for C function pointers.

All tests passed.