feat: auto detect cpu_num

drama/src/main.c

@@ -57,7 +57,7 @@ main(int argc, char **argv)
     size_t rounds    = ROUNDS_std;
     size_t m_size    = MEM_SIZE_std;
     size_t threshold = THRESHOLD_std;
-    size_t cpu       = 1;
+    size_t cpu       = 0;
     char *o_file     = (char *) O_FILE_std;
 
     flags |= F_POPULATE;