feat: "serde" feature flag

Cargo.toml

@@ -13,7 +13,11 @@ keywords = ["holiday", "Germany", "Feiertage"]
 [dependencies]
 chrono = "0.4"
 computus = "1.0.0"
-
+serde = { version = "1.0", features = ["derive"], optional = true }
 
 [dev-dependencies]
 proptest = "0.9.1"
+
+[features]
+default = []
+serde = ["dep:serde"]

src/holidays.rs

@@ -7,6 +7,7 @@ use computus;
 /// For public holidays use `GermanRegion` instead, since
 /// public holidays differ from region to region.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum GermanHoliday {
     Neujahr,
     HeiligeDreiKoenige,

src/regions.rs

@@ -5,6 +5,7 @@ use chrono::{Datelike, NaiveDate};
 /// Holidays guaranteed to take place on sundays, e.g. easter sunday, are excluded by default.
 /// However, holidays with a fixed date can still fall on a sunday.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum GermanRegion {
     BadenWuerttemberg,
     /// * The Augsburger Friedensfest only applies to Augsburg.
@@ -238,5 +239,4 @@ mod tests {
         assert!(BadenWuerttemberg.holidays_in_year(year).is_empty());
     }
     }
-
 }