Consider adding a distance and speed property to accessor

[sfmig]

From the kinematics tutorial PR review:

We could add a "distance" property in our accessor to access directly the distance travelled, e.g:

distance_travelled = ds.move.distance

Similarly with speed.

[sfmig]

Make a method instead of a property.
Nomenclature: ds.get_cumulative_distance() ?

[niksirbi]

Maybe ds.cumulative_displacement(from=0, to=100)? Because we will literally calculate it as cumsum of the displacement.

[niksirbi]

See exhaustive discussion in #162

[sfmig]

@niksirbi @lochhh seems like we can close this now?

[lochhh]

or edit this to add more convenience methods to the accessor, e.g. compute_speed, compute_distance_travelled as suggested here?

[niksirbi]

Yeah, i'd keep it open, because we may consider adding those convenience methods.

[niksirbi]

Consider calling distance "path length"

[niksirbi]

We've decided to refer to "distance travelled" as path_length, to avoid confusion with pairwise distances (see #277).

While implementing the compute_path_length() function, I encountered a dilemma on how to handle missing values, see discussion on zulip.