Implement a recursive get_block.

src/renderer/inline_partial_tree.rs

@@ -19,6 +19,16 @@ impl<'a> InlinePartialTreeElement<'a> {
             blocks: blocks,
         }
     }
+
+    pub fn get_block(&self, name: &str) -> Option<&'a Option<Body<'a>>> {
+        match self.blocks.get(name) {
+            None => match self.parent {
+                None => None,
+                Some(parent_tree_element) => parent_tree_element.get_block(name),
+            },
+            Some(interior) => Some(interior),
+        }
+    }
 }
 
 pub fn extract_inline_partials<'a>(