newestlog should have options returning other than the last log

```newestlog -2 barman``` would return the next to last barman log
```newestlog +2 barman``` would return the second oldest barman log
```newestlog ,+3 barman``` would return the three oldest barman logs
```newestlog ,-3 barman``` would return the oldest barman logs up to, and including, the third from newest
