Representation of the doy is implemented in a more flexible way and offers two choices: mw and mw5d (fixes #82)

A new more flexible method to define the timestep indices belonging to the different doy is implemented. This method can be used both for the calibrate and the adjust step. At the moment, the method offers two different variants for the moving window: mw and mw5d. mw is a moving window with 31d window width and 1-day iteration step. mw5d has also 31d window width but a 5-day iteration step between the moving windows. In the mw5d mode, the first doy will be on January 1, the second on January 6 etc.