Flexible DOY definition

This merge requests adds functionality to choose whether to use the previous DOY representation with 365 steps per year or a new implementation 'mw5d' that moves the moving window in steps of 5 days through the annual cycle, thereby reducing the computational load. Also a monthly representation is built in but is prevented from being used due to problems with unequal shapes of dask-arrays when stacking them. The DOY representation is controled by the command flag -D or --doytype which can be either mw (standard moving window) or mw5d (5-day-steps between moving windows).