Enable Message Markup parsing in newly-created sub-boards by default

Message Markup seems to be working well, so just enable by default on newly created subs (existing sub-boards aren't impacted). A sysop can always disable this option on a per sub-board basis if its a problem.

src/sbbs3/scfg/scfgsub.c

@@ -36,6 +36,7 @@ bool new_sub(unsigned new_subnum, unsigned group_num, sub_t* pasted_sub, long mi
 	new_subboard->misc |= misc;
 	if(new_subboard->misc&(SUB_FIDO | SUB_INET))
 		new_subboard->misc |= SUB_NOVOTING;
+	new_subboard->pmode = P_MARKUP;
 	new_subboard->maxmsgs = 500;
 
 	/* Use last sub in group (if exists) as a template for new subs */