[Suggestion] Pretty print of ARC-Authentication-Results

[ro78]

Hello,

This is not a bug at all, just a cosmetic thing.

When my authentication results look like this:

Authentication-Results: my.fqdn.com;
	dkim=none;
	spf=pass (my.fqdn.com: domain of noreply@sender.com designates X.X.X.X as permitted sender) smtp.mailfrom=noreply@sender.com;
	dmarc=pass (policy=none) header.from=sender.com

My ARC-Authentication-Results look liks this:

ARC-Authentication-Results: i=1; my.fqdn.com; dkim=none;
	spf=pass smtp.mailfrom=noreply@sender.com;
	dmarc=pass header.from=sender.com;
	arc=none smtp.remote-ip=X.X.X.X

But I would find it easier to read like this (like Google does):

ARC-Authentication-Results: i=1; my.fqdn.com;
	dkim=none;
	spf=pass smtp.mailfrom=noreply@sender.com;
	dmarc=pass header.from=sender.com;
	arc=none smtp.remote-ip=X.X.X.X

In arc.c line 3485:

arc_dstring_printf(dstr, "; %s", ar);

Changing it to

arc_dstring_printf(dstr, ";\r\n\t%s", ar);

Seems to work to put dkim back on new line.

What do you think?