Moved application settings to settings_t struct

Since logfp, oldstyle, and prompt were application settings, rather than
have them all as global vars, move them to a single global var, seperate
from game state, as they aren't, technically, game state, but are
application settings.

cheat.c

@@ -10,10 +10,6 @@
 #include <stdbool.h>
 #include "advent.h"
 
-FILE *logfp = NULL;
-bool oldstyle = false;
-bool prompt = true;
-
 int main(int argc, char *argv[])
 {
     int ch;