Implement is_empty in addition to len

Author: michaelklishin

src/transformers.rs

@@ -112,4 +112,8 @@ impl TransformationChain {
     pub fn len(&self) -> usize {
         self.chain.len()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.chain.is_empty()
+    }
 }