Add astronomical calculations

[mannylopez]

Closes #6 #11

Based on

• https://aa.quae.nl/en/reken/hemelpositie.html and
• https://github.com/mourner/suncalc which looks to be based off of https://github.com/microsoft/AirSim/blob/main/AirLib/include/common/EarthCelestial.hpp

AstronomicalConstant

• Add a new namespace, AstronomicalConstant, for all astronomical calculations
• Add getMoonPhase and supporting functions
  • degreesToRadians
  • radiansToDegrees
  • declination
  • rightAscension
  • moonCoordinates
  • solarMeanAnomaly
  • eclipticLongitude
  • sunCoordinates
  • daysSinceJ2000
• Add tests for all methods
• Document all methods