Issue #362 - Added the option for showing the file name along with the logs

Hi.
With this tweak, one will be able to print the file name along with the logs with the option 'showFileName' set to true.
```javascript
new (winston.Logger)({
    exitOnError: false,
    transports: DEFAULT_TRANSPORTS,
    'showFileName': true
});
```

This is how the logs would look-
```properties
2014-04-29T07:14:57.720Z - debug: [/home/user/project/trunk/someFolder/server/app.js] Logging module 'Winston' has been successfully integrated.
```

In order to achieve this I have modified the following files:
#	modified:   lib/winston/common.js
#	modified:   lib/winston/logger.js
#	modified:   lib/winston/transports/console.js
#	modified:   lib/winston/transports/daily-rotate-file.js
#	modified:   lib/winston/transports/file.js
#	modified:   lib/winston/transports/http.js
#	modified:   lib/winston/transports/memory.js
#	modified:   lib/winston/transports/webhook.js

Please let me know, if this pull can be approved.

Thanks,
Gaurav