feat: Iter struct

src/elements/list.rs

@@ -60,6 +60,8 @@ impl List {
     }
 }
 
+#[cfg_attr(test, derive(PartialEq))]
+#[derive(Debug)]
 pub struct ListItem<'a> {
     pub bullet: &'a str,
 }

src/elements/mod.rs

@@ -47,6 +47,7 @@ pub use self::{
 
 #[derive(Debug)]
 pub enum Element<'a> {
+    Root,
     Block {
         block: Block<'a>,
         begin: usize,