Added operator= integer operator.

testing/mstring_test.cpp

@@ -88,7 +88,12 @@ int main(int argc, char **argv) {
    coreutils::MString test26;
    double test27 = 4.0f;
    test26 = test27;
-   std::cout << "float: " << test26 << std::endl;   
+   std::cout << "float: " << test26 << std::endl;
+
+   coreutils::MString test28;
+   int test29 = 402;
+   test28 = test29;
+   std::cout << "int: " << test28 << std::endl;
    
    return 0;
 }