rename api, add cc and bcc, handle multiple players

rename: src -> from, dst -> to

api.md

@@ -2,6 +2,25 @@
 # Mail format
 The mail format in the api hooks
 
+```lua
+mail = {
+	from = "sender name",
+	to = "players, which, are, addressed",
+	cc = "carbon copy",
+	bcc = "players, which, get, a, copy, but, are, not, visible, to, others",
+	subject = "subject line",
+	body = "mail body",
+	-- 8 attachments max
+	attachments = {"default:stone 99", "default:gold_ingot 99"}
+}
+```
+
+The fields `to`, `cc` and `bcc` can contain a player, multiple player names separated by commas, or be empty. Players in `to` are the recipiants, who are addressed directly. `cc` specifies players that get the mail to get notified, but are not immediate part of the conversation. There is no technical difference between `to` and `cc`, it just implies meaning for the players. Players can see all fields making up the mail except `bcc`, which is the only difference to `cc`.
+
+Attachments need to be provided for each player getting the mail. Until this is implemented, trying to send a mail to multiple players will fail.
+
+The `from` and `to` fields were renamed from the previous format:
+
 ```lua
 mail = {
 	src = "source name",
@@ -22,8 +41,10 @@ mail.send("source name", "destination name", "subject line", "mail body")
 New variant (1.1+)
 ```lua
 mail.send({
-	src = "source name",
-	dst = "destination name",
+	from = "sender name",
+	to = "destination name",
+	cc = "carbon copy",
+	bcc = "blind carbon copy",
 	subject = "subject line",
 	body = "mail body"
 })