Adds simple delete api

cookbook/src/bin/write_recipe.rs

@@ -76,7 +76,7 @@ fn main() {
     }
     let mut category_id = String::new();
     stdin().read_line(&mut category_id).unwrap();
-    let category_id = category_id.trim().parse::<i16>().expect("Could not parse id");
+    let category_id = category_id.trim().parse::<i16>().unwrap_or(0);
     builder.set_category(category_id);
 
     println!("Ingredients (empty line to finish): ");