Interface to resume simulations

[jhauschild]

At the moment, when a simulation aborts one needs to resume from the checkpoint by explicitly passing the filename of the checkpoint to tenpy.resume_from_checkpoint (an alias for tenpy.simulations.simulation.resume_from_checkpoint).

• With the cluster_jobs.py in the template project repo, this can be done quite easily, but there's no example - add that!
• On the other hand, it's also not hard to add another entry point from the command line to the setup.py, such that something like tenpy-resume checkpoint.h5 works
• It might be convenient to be able to pass the original yaml file to tenpy-resume as well, such that it figures out filenames itself, checks whether the simulations ran, and then continues the first one that didn't finish. This is a bit problematic, though, if the filename changed to not overwrite existing files - which is the default. Is there a good way to handle that case?

See also this forum topic