Function covid19db::dateutil::ymd_to_jd

pub fn ymd_to_jd(year: i32, month: u32, day: u32) -> JulianDay

Convert a year, month, day to a JulianDay

use covid19db::dateutil::*;
use chrono::prelude::*;
use julianday::JulianDay;

assert_eq!(ymd_to_jd(2015, 3, 14), JulianDay::new(2457096));