Add a full-document parse benchmark.

src/parser/document.rs

@@ -208,3 +208,17 @@ fn _document<'b, 'g, 'r, 's>(
         },
     ))
 }
+
+#[cfg(test)]
+mod tests {
+    use test::Bencher;
+
+    use super::*;
+
+    #[bench]
+    fn bench_full_document(b: &mut Bencher) {
+        let input = include_str!("../../org_mode_samples/element_container_priority/README.org");
+
+        b.iter(|| assert!(parse(input).is_ok()));
+    }
+}