Add ssh2sshng.py utility for converting ssh hashes into sshng hashes

For testing you can use the following steps,

```
✗ python ../run/ssh2sshng.py unused/sshdump > sshngdump
✗ ../run/john sshngdump 
Loaded 2 password hashes with 2 different salts (ssh-ng SSH RSA / DSA [32/64])
12345            (rsa_test.key)
12345            (dsa_test.key)
...
guesses: 4  time: 0:00:00:01 0.00% (3)  c/s: 319823  trying: 0101996
```

I was too lazy to add this functionality into the sshng format itself.