This sub-system contains functions to search for granules and get their
filenames, as well as functions to read particular datasets and rearrange the
data is a predefined manner.

This requires configurations and defaults via datasets_config and
datasets_defaults.

The files common_read_* have the task to read a particular granule from a
particular dataset and arrange it in a structure that contains at least lat,
lon and time, where the number of rows in each three should be the same, and
the number of columns in lat and lon should be equal, and the number of
columns in time should be 1. This convention was initially designed for the
portable use of collocation codes. E.g. if one wants to add a new dataset to
be collocated with others, one needs to add a reader function in the same
format and add the appropiate setting to datasets_constants.

For instructions on adding new datasets, see the help of datasets_config.