astrog improvements

[veenstrajelmer]

Todo:

• astrog time-related improvements #332
• add test for astrog difference plot #338
• astrog datetime index instead of column #346
• when calling hatyan.astrog.astrog_culminations(tFirst="18870101",tLast="20221231") it raises "Exception: Requested time out of range (1900-2091)". This is not necessary to change, but would be convenient anyway, e.g. for Support pre-1900 timeseries for calc_HWLW_springneap() Deltares-research/kenmerkendewaarden#184 >> Astrog support for pre-1900 timestamps #420
• astrog_moonriseset fails for some longitudes #323
• astrog reproduction works, but not everything works for all coordinates
• consider moving to pyephem or other python astro package (of astropy of pint voor units)
• https://mathematica.stackexchange.com/questions/291855/calculating-upper-culmination-of-the-moon
• consider moving astrog to separate package