logger implementation using custom api

This is the change to add logger implementation using freedom 0.5.0 custom api support. 
I think it's good to include the explicit return type... i.e.  for this case:
```
private doRealLog = (
 +        level: string, tag: string, msg: string, args: any[]) : void => {
```

Can you do this for other functions too? Thx!