refactor: splitting models

docs/guide/first_exam.md

@@ -226,7 +226,8 @@ Assembling a form programmatically:
 use std::collections::BTreeMap;
 use std::path::Path;
 
-use coursebank::assessment::{Blueprint, History};
+use coursebank::assessment::Blueprint;
+use coursebank::history::History;
 use coursebank::date::Date;
 use coursebank::{select, Catalog, Level};