[REQ] option for write blank line between sub block

How about option for blank line between sub block?

from
```
1
00:00:09,012 --> 00:00:11,097
abcde
2
00:00:11,797 --> 00:00:13,925
fghi
```
to
```
1
00:00:09,012 --> 00:00:11,097
abcde

2
00:00:11,797 --> 00:00:13,925
fghi
```

Thanks.