Solar zenith formula

[bobzsu]

@BSchilperoort coming back to the issue with the solar zenith angle and solar azimuth - this paper gives a better solution with codes.
https://www.sciencedirect.com/science/article/pii/S0960148121004031

(According to the Almanac, the errors of the right ascension and
declination of the Sun given by these formulas are less than (1/60)�,
and the error of the equation of time is less than 3.5 s, if the input
year is between 1950 and 2050.)

[SarahAlidoost]

relates to #134