Change foreign key relationships to be ON DELETE CASCADE by default.

microrm/src/model/create.rs

@@ -159,7 +159,7 @@ pub fn sql_for_table<T: crate::model::Entity>() -> (String, String) {
 
         let fk = fk.map(|x| {
             format!(
-                " references \"{}\"(\"{}\")",
+                " references \"{}\"(\"{}\") ON DELETE CASCADE",
                 x.foreign_table_name(),
                 x.foreign_column_name()
             )