rewrite Output::write_line to fix indentation

Simplify (maybe?) the code in Output::write_line -- or at least, change
it so that it now works.

Update lists to use the new code.

Cargo.toml

@@ -12,3 +12,4 @@ serde_json = "1.0"
 serde_yaml = "0.9"
 regex = "1.10.4"
 log = "0.4.21"
+indoc = "2"

src/fmt_md.rs

@@ -13,12 +13,8 @@ where
     N: Borrow<MdqNode>,
     W: Write,
 {
-    let mut iter = nodes.iter().peekable();
-    while let Some(node) = iter.next() {
+    for node in nodes {
         write_one_md(out, node.borrow());
-        if iter.peek().is_some() {
-            write_one_md(out, &MdqNode::ThematicBreak)
-        }
     }
 }
 
@@ -70,8 +66,8 @@ where
                         prefix.push(if *checked { 'x' } else { ' ' });
                         prefix.push_str("] ");
                     }
+                    out.write_str(&prefix);
                     out.with_block(Inlined(prefix.len()), |out| {
-                        out.write_str(&prefix);
                         write_md(out, &item.item);
                     });
                 }