Implement FromStr for IString (#21)

Co-authored-by: Cecile Tonglet <cecile.tonglet@cecton.com>

src/string.rs

@@ -1,5 +1,6 @@
 use std::borrow::Cow;
 use std::fmt::Debug;
+use std::str::FromStr;
 
 /// An immutable string type inspired by [Immutable.js](https://immutable-js.com/).
 ///
@@ -147,6 +148,13 @@ impl std::borrow::Borrow<str> for IString {
     }
 }
 
+impl FromStr for IString {
+    type Err = std::convert::Infallible;
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        Ok(IString::from(String::from(value)))
+    }
+}
+
 #[cfg(feature = "serde")]
 impl serde::Serialize for IString {
     fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {