feature: timestamp prefix of `pm2.log`

Coverage(JSON/JS):
```
ls
start
restart
stop
kill
```

e.g.:
```
2014-11-29T11:36:35+08:00: [PM2][WORKER] Started with refreshing interval: 30000
2014-11-29T11:36:35+08:00: [[[[ PM2/God daemon launched ]]]]
2014-11-29T11:36:35+08:00: BUS system [READY] on port /Users/tjatse/.pm2/pub.sock
2014-11-29T11:36:35+08:00: RPC interface [READY] on port /Users/tjatse/.pm2/rpc.sock
2014-11-29T11:36:35+08:00: PM2 is being killed via kill method
2014-11-29T11:36:35+08:00: RPC socket closed
2014-11-29T11:36:35+08:00: PUB socket closed
```