add built-in hexdump to bsnprintf()

add built-in hexdump to bsnprintf()

- sample
char hash[MAX_HASH_SIZE];
int hash_size=32;

/* notice that the length is the length in the output "buffer" not the
   length of the input buffer. This is like in any printf() "length"
   any char in the input will generate 2 digit in the output, you must
   multiply by 2 the size of the input buffer or get a small output!
   It is safe because bnsprintf() knows the length of its output buffer
   and truncate any overload
*/
Mmsg(0, "the hash is :%64W", hash);             // fixed size
Mmsg(0, "the hash is :%*W", 2*hash_size, hash); // variable size