Allow the json::builder::ObjectBuilder to insert &str keys

src/json/builder.rs

@@ -56,9 +56,9 @@ impl ObjectBuilder {
         Object(self.object)
     }
 
-    pub fn insert<T: ToJson>(self, key: String, value: T) -> ObjectBuilder {
+    pub fn insert<K: StrAllocating, V: ToJson>(self, key: K, value: V) -> ObjectBuilder {
         let mut builder = self;
-        builder.object.insert(key, value.to_json());
+        builder.object.insert(key.into_string(), value.to_json());
         builder
     }
 

src/json/value.rs

@@ -639,3 +639,9 @@ impl<A:ToJson> ToJson for Option<A> {
         }
     }
 }
+
+impl<'a, T: ToJson> ToJson for &'a T {
+    fn to_json(&self) -> Value {
+        (*self).to_json()
+    }
+}