Add filter by time in ncextract and catchstats

[casadoj]

Currently these two functions read all the NetCDF files contained in the specified folder. It could be interesting to add two attributes to define the start and end of the period of interest.

Example:
The results of the GloFAS long run are saved in yearly files from 1979 to present. If I want to extract the time series of the GloFAS long run for the period 1991-2020, I could use these attributes to reduce the amount of data processing.
This would be very interesting to skip the warm-up period of the long runs.