Add support for a configuration file

src/config.rs

@@ -0,0 +1,21 @@
+use std::path::PathBuf;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Deserialize, Serialize)]
+pub(crate) struct Config {
+    pub(crate) server_url: String,
+    pub(crate) api_key: String,
+
+    pub(crate) people: People,
+}
+
+#[derive(Deserialize, Serialize)]
+pub(crate) struct People {
+    pub(crate) sync_date_of_births: SyncDateOfBirths,
+}
+
+#[derive(Deserialize, Serialize)]
+pub(crate) struct SyncDateOfBirths {
+    pub(crate) vcard: PathBuf,
+}