Change seed_curves_from_lambda_max to use parameter name-value pairs
for optional inputs.

Commit fixes bug whereby odeSolverOptions was overwritten by
hard-written value.
Make periodic boundary condition optional for poincare_closed_orbit
Change poincare_closed_orbit_multi to use name-value pairs for
optional inputs.
Improve comment
Analyze η₊ and η₋ when detecting closed orbits in double gyre demo