option to store the command line arguments in the file name

An option (-a --args-in-filename) to embed the command line into the log file name.
```
justlog -a barman -v backup --wal-transfer alternate/mtv-pg-01
```
Would yield something like this:
```
~/tmp/justlog___barman_-v_backup_--wal-transfer_alternate__mtv-pg-01-2019-11-12T21:20:19
```