Improve error message for trajectory invalid attribute in map display
Trajectory
objects with an invalid property in map display reports a cryptic ValueError
message:
>>> fig = plt.figure(figsize=(12, 6))
>>> ax = fig.add_subplot(projection=EUROPA)
>>> ax.plot(traj, 'foo')
ValueError: Unrecognized character f in format string
This MR should provide a better error message:
ValueError: The second argument `foo` must be a `Trajectory` property
or a valid matplotlib format string (eg. `ro`).
Edited by Benoit Seignovert