Fetches holidays for a given country and year.

Examples

iex> Calendarific.holidays(country: "US", year: 2021)
[
  %Calendarific.Types.Holiday{
    country: %Calendarific.Types.Country{id: "us", name: "United States"},
    date: %Calendarific.Types.Date{
      datetime: %Calendarific.Types.DateTime{day: 1, month: 1, year: 2021},
      iso: "2021-01-01"
    },
    description: "New Year's Day is the first day of the Gregorian calendar, which is widely used in many countries such as the USA.",
    locations: "All",
    name: "New Year's Day",
    states: "All",
    type: ["National holiday"]
  }
  ...
]