Add method for getting object refs of top-level objects of chunk (#40)

Author: LaurenzV

src/chunk.rs

@@ -47,6 +47,12 @@ impl Chunk {
             .extend(other.offsets.iter().map(|&(id, offset)| (id, base + offset)));
     }
 
+    /// An iterator over the references of the top-level objects
+    /// of the chunk, in the order they appear in the chunk.
+    pub fn refs(&self) -> impl IntoIterator<Item = Ref> + '_ {
+        self.offsets.iter().map(|&(id, _)| id)
+    }
+
     /// Renumbers the IDs of indirect objects and all indirect references in the
     /// chunk and returns the resulting chunk.
     ///