/**

@page page_dialog Dialog system

The dialog system used by NPCs and magic ear works in the following way:
- the message is stored in the obj::msg field
- the first time the NPC is talked to, this structure is parser to the
obj::dialog_information field
- this field contains all information needed to know what words the NPC reacts too.

The core dialog is in communicate().

When a player talks, there are two cases:
- said text is a reply for an NPC. In this case, the display of the actual's player message is done in
do_talk_npc() based on the reply
- when the text doesn't match anything, the display is done in communicate() directly.

This enables special things like 'Player asks: What is this?'.

The following tags can be used in the obj::msg field:
- <code>\@match xxx</code> introduces a dialog message. <code>xxx</code> can be either '*' or a regexp,
with | to separate alternatives
- <code>\@reply value text</code> is one possible reply the player can give to the message. <code>value</code>
is what the player should say (using <code>say value</code>), <code>test</code> is what will be actually displayed
- <code>\@question value text</code> is the same as \@reply except the player will ask <code>text</code>

Note that <code>value</code> can't contain spaces.

@todo
- update dialog_information when msg changes.
- have a real regexp parser
*/