Set up code structure for lesser blocks.

src/parser/lesser_block.rs

@@ -0,0 +1,11 @@
+use super::error::Res;
+use super::Context;
+use crate::parser::lesser_element::LesserBlock;
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn lesser_block<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, LesserBlock<'s>> {
+    todo!()
+}