Eliminate calls to sprintf

Apple Xcode has started giving `-Wdeprecated-declarations` warnings
for `sprintf`, and suggesting that people migrate to `snprintf` instead.
This is silly, but the warnings are spam and need to be silenced
somehow. Migrating to `snprintf` and/or `hr::format` is the path of
least resistance.

quit.cpp

@@ -27,9 +27,7 @@ EX int getgametime() {
   }
 
 EX string getgametime_s(int timespent IS(getgametime())) {
-  char buf[20];
-  sprintf(buf, "%d:%02d", timespent/60, timespent % 60);
-  return buf;
+  return hr::format("%d:%02d", timespent/60, timespent % 60);
   }
 
 EX bool display_yasc_codes;