check_constraint and update_state functions are created inside
create_automaton_*(), by the evaluation of meta_elementary_functions <:
Expr. check_constraint and update_state don't depend on constants::Dict
anymore: constants are interpolated inside the expression.

Add of tests for euclidean distance automaton.
Add a new function euclidean_distance that computes the euclidean
distance of a Trajectory compared to observations along a discrete
timeline.

- A_per (period_automaton) computes noisy period of an oscillatory model
- A_eucl (euclidean_distance) computes euclidean distance with regard to
data points of a trajectory.

1 script that plots oscillatory trajectory is added