Add the code structure for planning.

src/parser/planning.rs

@@ -0,0 +1,8 @@
+use super::Context;
+use crate::error::Res;
+use crate::parser::lesser_element::Planning;
+
+#[tracing::instrument(ret, level = "debug")]
+pub fn planning<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Planning<'s>> {
+    todo!()
+}