moonlit 0.1.0

• Initial CRAN release.
• Implemented calculateMoonlightIntensity() function for predicting moonlight intensity on the ground for any given place and time.
• Implemented calculateMoonlightStatistics() function for calculating nightly statistics of moonlight illumination and moon phase.
• Added elevExtCoeff() function to calculate extinction coefficient based on elevation.
• Incorporated twilight illumination prediction.