Change function chunk_indices() to get_chunk_indices() because chunk_indices is an item in some functions

Start() can correctly merge files along the dimension that has different length each file, without additional NAs.

Deprecate 'crop' in CDORemapper() and add variable 'crop_domain' for automatically generating 'crop'

Deprecate 'crop' in CDORemapper(). It is automatically assigned as the borders of lat/lon selectors in Start() call. (WIP)