feat: implement FromStr for Timeout

Useful when wanting to pass it as a command line argument to an
application.

src/timeout.rs

@@ -1,3 +1,5 @@
+use std::{num::ParseIntError, str::FromStr};
+
 /// Describes the timeout of a notification
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Timeout {
@@ -55,6 +57,18 @@ impl From<Timeout> for i32 {
     }
 }
 
+impl FromStr for Timeout {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "default" => Ok(Timeout::Default),
+            "never" => Ok(Timeout::Never),
+            milliseconds => Ok(Timeout::Milliseconds(u32::from_str(milliseconds)?)),
+        }
+    }
+}
+
 pub struct TimeoutMessage(Timeout);
 
 impl From<Timeout> for TimeoutMessage {