Make lots of generic data parameters into 'void *'.

This is a cleanup I started to notice a need for during the BinarySink
work. It removes a lot of faffing about casting things to char * or
unsigned char * so that some API will accept them, even though lots of
such APIs really take a plain 'block of raw binary data' argument and
don't care what C thinks the signedness of that data might be - they
may well reinterpret it back and forth internally.

So I've tried to arrange for all the function call APIs that ought to
have a void * (or const void *) to have one, and those that need to do
pointer arithmetic on the parameter internally can cast it back at the
top of the function. That saves endless ad-hoc casts at the call
sites.

sshblowf.h

@@ -9,7 +9,6 @@ void *blowfish_make_context(void);
 void blowfish_free_context(void *handle);
 void blowfish_initkey(BlowfishContext *ctx);
 void blowfish_expandkey(BlowfishContext *ctx,
-                        const unsigned char *key, short keybytes,
-                        const unsigned char *salt, short saltbytes);
-void blowfish_lsb_encrypt_ecb(unsigned char *blk, int len,
-                              BlowfishContext *ctx);
+                        const void *key, short keybytes,
+                        const void *salt, short saltbytes);
+void blowfish_lsb_encrypt_ecb(void *blk, int len, BlowfishContext *ctx);