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
• 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)
• consider moving astrog to separate package