establish dask-mpi batch processing functionality

[matt-long]

Based on a discussion today, I think we want to have a batch processing capability in esmlab based on dask-mpi.

All the functions in esmlab.climatology accept and return arguments of type xr.Dataset; explicit attention has been paid to ensure that the returned Dataset is suitable to write to file (attributes and dtypes preserved, etc.).

@kmpaul, @andersy005: can you please provide @alperaltuntas with a dask-mpi example?

cc: @mnlevy1981, @jukent

[andersy005]

@alperaltuntas, is https://github.com/alperaltuntas/mncPy the repo with the scripts you mentioned?