add split string to vector int

tests/string.cpp

@@ -14,3 +14,9 @@ TEST(split_str, check)
   ASSERT_EQ(hack::string::split_str("qqq,aaa:eee,sss", ":,"), v1);
 
 }
+
+TEST(split_stoi, check)
+{
+  std::vector<int> v { 1, 2, 3 };
+  ASSERT_EQ(hack::string::split_stoi("1 2 3", ' '), v);
+}