Add support for cracking Password Safe files

I have added support for cracking Password Safe files to hashkill.

Test File: Extract sample Password Safe file from http://openwall.info/wiki/_media/john/Sample-Password-Safe-Safes.tar archive.

```
hashkill --plugin pwsafe -f ~/pwsafe-openwall.psafe3 -r dictionary -a ~/wordlist

[hashkill] Version 0.3.1
[hashkill] Scheduler initialized.
[hashkill] Plugin 'pwsafe' loaded successfully
[hashkill] Rule based attack, using rule:dictionary
[hashkill] File pwsafe-openwall.psafe3 loaded successfully
[hashkill] CPU features: SSE2 SSE3
[hashkill] Detected 8 CPUs.
[hashkill] Spawned 8 threads.
[hashkill] Attack has O(n) complexity
[hashkill] Initialized hash bitmaps


[hashkill] -= Cracked list =-

Username: 		Hash: 					Preimage:
-----------------------------------------------------------------------------------
 pwsafe-openwall	Password Safe pwsafe file                	openwall             

[hashkill] Total: 1 passwords cracked

[hashkill] Attack took 0 seconds.
[hashkill] Bye bye :)

```

It would be great if someone could port this plug-in to OpenCL and use SIMD in the CPU version.