Renamed DAYBYTES to USEDCDT (amount of free credits used today)

DAYBYTES is now an alias for BTODAY, since that more accurately reflects what
PCB and WC used this code for, though WC4 Sysop Guide says it's in "K", we'll
ignore that inconsistency (Wildcat! docs are wrong maybe?).

src/sbbs3/atcodes.cpp

@@ -1330,7 +1330,8 @@ const char* sbbs_t::atcode(const char* sp, char* str, size_t maxlen, int* pmode,
 		return str;
 	}
 
-	if (strcmp(sp, "BTODAY") == 0) {
+	// Note: @DAYBYTES@ = "Daily download K" in Wildcat 4 Sysop Guide, but "Number of bytes downloaded today" in PCBoard v15.2 Sysop Manual
+	if (strcmp(sp, "BTODAY") == 0 || strcmp(sp, "DAYBYTES") == 0) {
 		safe_snprintf(str, maxlen, "%" PRIu64, useron.btoday);
 		return str;
 	}
@@ -1505,7 +1506,7 @@ const char* sbbs_t::atcode(const char* sp, char* str, size_t maxlen, int* pmode,
 		return str;
 	}
 
-	if (!strcmp(sp, "DAYBYTES")) {    /* amt of free cdts used today */
+	if (!strcmp(sp, "USEDCDT")) {    /* amt of free cdts used today */
 		safe_snprintf(str, maxlen, "%" PRIu64, cfg.level_freecdtperday[useron.level] - useron.freecdt);
 		return str;
 	}