Added a chat history plugin.

The mod_chat_history plugin provides chat history for all public chat messages.

Can be configured in the following ways:

- history_max: max number of messages stored in history
- history_default: the default number of messages to be returned when invoking !history
- history_connect: if > 0, then this number of messages is automatically sent when connecting to the hub

Removed the built-in !history command in favour of the mod_chat_history plug-in.

Make sure we unescape all chat messages before forwarding any of them to plugins.

Update example plugins.conf in documentation directory.

src/core/hub.h

@@ -109,7 +109,6 @@ struct hub_info
 	char* recvbuf; /* Global receive buffer */
 	char* sendbuf; /* Global send buffer */
 
-	struct linked_list* chat_history;    /* Chat history */
 	struct linked_list* logout_info;     /* Log of people logging out. */
 
 	struct command_base* commands;       /* Hub command handler */
@@ -151,16 +150,6 @@ extern int hub_handle_password(struct hub_info* hub, struct hub_user* u, struct
  */
 extern int hub_handle_chat_message(struct hub_info* hub, struct hub_user* u, struct adc_message* cmd);
 
-/**
- * Add a chat message to the chat history
- */
-extern void hub_chat_history_add(struct hub_info* hub, struct hub_user* user, struct adc_message* cmd);
-
-/**
- * Clear the chat history.
- */
-extern void hub_chat_history_clear(struct hub_info* hub);
-
 /**
  * Used internally by hub_handle_info
  * @return 1 if nickname is OK, or 0 if nickname is not accepted.