Add an option that makes it possible to ensure that the last point is exactly for Tmax; make sure that we never exceed Tmax

Why the ` / 2?` We don't care about closeness, we care about not overshooting. If
```
parameters.tmax - parameters.Δt / 2 >= tn && tn > parameters.tmax - parameters.Δt
```
this condition will be false, h will be `parameters.Δt` and the integration step will overshoot `parameters.tmax`.