put something meaningful instead of C65 DOS version string

src/dos_m65/4010.dos_datestr.s

@@ -0,0 +1,7 @@
+
+; A replacement for the original 'VYYMMDD' version string
+
+!pet "o"         ; to mark this is Open ROMs
+!pet "xxxxxx"    ; date, in YYMMDD format
+!pet "xx"        ; two most significand digits of the year
+!pet "       "   ; reserved for future use