Add new generation algorithm

The scrypt-genpass compatible one is now the legacy algorithm
(activated with -L or --legacy).

LegacyPasswordGenerator.h

@@ -20,21 +20,13 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#import <ObjFW/ObjFW.h>
+#import "PasswordGenerator.h"
 
-@interface LegacyPasswordGenerator: OFObject
+@interface LegacyPasswordGenerator: OFObject <PasswordGenerator>
 {
 	size_t _length;
 	OFString *_site;
 	const char *_passphrase;
 	unsigned char *_output;
 }
-
-@property size_t length;
-@property (copy) OFString *site;
-@property const char *passphrase;
-@property (readonly) unsigned char *output;
-
-+ (instancetype)generator;
-- (void)derivePassword;
 @end