Attempts to add a syslog-based mecanism

Warning: this PR includes the previous one (#439)

This adds support for timestamp, process ID, and other useful information provided by syslog. What we can expect to have:

```
$ sudo tail -f /var/log/vishnu.log 
Apr  9 17:51:54 tchieudjie vishnu[5681]: [WARN] Not registered in dispatcher
Apr  9 17:52:25 tchieudjie vishnu[11219]: [INFO] Parsing the uri (tcp://127.0.0.1:5565)...
Apr  9 17:52:25 tchieudjie vishnu[11219]: [INFO] Parsing the uri (tcp://127.0.0.1:5561)...
Apr  9 17:52:25 tchieudjie vishnu[11219]: [ERROR] zmq socket_server (tcp://127.0.0.1:5565) binding failed (Address already in use)
Apr  9 17:52:37 tchieudjie vishnu[11260]: [INFO] Parsing the uri (tcp://127.0.0.1:5565)...
Apr  9 17:52:37 tchieudjie vishnu[11260]: [INFO] Parsing the uri (tcp://127.0.0.1:5561)...
Apr  9 17:52:37 tchieudjie vishnu[11260]: [INFO] ZMQ socket bound (tcp://127.0.0.1:5565)
```