tangfu 5af24314c3 add front and back (#269)
* add front and back

i'll get the last message in some situations,but have to do like this :
```
multimsg msgs;
auto msg = msgs[msgs.size() - 1];
func(msg.size());
auto *msg = msgs.end() - 1;
```
but, std::queue have some method 'front' and 'back'. so maybe i can simply do this ? :
```
multimsg msgs;
auto msg = msgs.back();
```

* add test for front and back
2018-10-17 08:41:21 +01:00
..
2018-10-17 08:41:21 +01:00