usage を入れて CPU とメモリを計測できるように

こんな感じでログが出る

```
   info  - socket.io started
[2014-02-05 23:27:05.609] [INFO] BeamQuest - development
[2014-02-05 23:27:05.653] [INFO] BeamQuest - development
[2014-02-05 23:27:05.714] [INFO] BeamQuest - start
[2014-02-05 23:27:06.726] [DEBUG] BeamQuest - cpu: 2.5, memory: 32022528
[2014-02-05 23:27:07.729] [DEBUG] BeamQuest - cpu: 1, memory: 32124928
[2014-02-05 23:27:08.733] [DEBUG] BeamQuest - cpu: 0.5, memory: 32215040
[2014-02-05 23:27:09.734] [DEBUG] BeamQuest - cpu: 1, memory: 32342016
[2014-02-05 23:27:10.739] [DEBUG] BeamQuest - cpu: 0.5, memory: 32419840
```