Added functions to flag Lunar Rise/Set as Valid or not

Release adds functions to flag a computed Moon Rise or Moon Set time as valid for the day provided. This is because some days will not have a Moon Rise or Moon Set time on that date, as the Moon progresses in its' orbit around the Earth.

What's Changed

• Add implementation of Moon valid rise/set flags by @DavidArmstrong in #13

Full Changelog: v1.4.0...v1.5.0