Add dynamic_insert_into test.

tests/mysql/usage/SampleTest.cpp

@@ -111,6 +111,11 @@ int main()
     db(update(tab).set(tab.gamma = false).where(tab.alpha.in(sqlpp::value_list(std::vector<int>{1, 2, 3, 4}))));
     db(update(tab).set(tab.gamma = true).where(tab.alpha.in(1)));
 
+    // dynamic insert
+    auto dynin = dynamic_insert_into(db, tab).dynamic_set(tab.gamma = true);
+    dynin.insert_list.add(tab.beta = "cheesecake");
+    db(dynin);
+
     // remove
     db(remove_from(tab).where(tab.alpha == tab.alpha + 3));