v1.6

1. Acoustic emissions: The linked list carrying the emission nodes can now be pruned based on a user-defined function.
2. Kirkwood-Bethe hypothesis: Changes to how the computation and update of the invariant f are implemented, to make the explicit velocity expression compatible with the recently introduced shock treatment method.
3. Examples: Corrected reference solution for the spherical acoustic emitter example.
4. Documentation: Updates and corrections.