Creation of automata has been change again to improve performance. Now
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.