7z support

[Rolf]

Some limitations in current implementation:

1. Currently, hc uses 7z2john (available from the mumbo jumbo fork of jtr), and sometimes (a lot of different file types in the archive) fails to load the hash, which turns out to be oh so long.
   
2. Since the hash itself doesn't have any archived & encrypted data for verification, hc will not stop once a password has been found (it's a feature).