mod_vcard_muc: Add an alternative method of signaling avatar change When the avatar has been changed, a signal is sent that the room configuration has changed. Clients then do a disco#info query to find the SHA-1 of the new avatar. They can then fetch it as before, or not if they have it cached already. This is meant to be less disruptive than signaling via presence, which caused problems for some clients. If clients transition to the new method, the old one can eventually be removed. The namespace is made up while waiting for standardization. Otherwise it is very close to what's described in https://xmpp.org/extensions/inbox/muc-avatars.html

# Introduction

This module adds support for advertising the language used in a room.

# Configuring

``` {.lua}
Component "rooms.example.net" "muc"
modules_enabled = {
    "muc_lang";
}
```

The room language is specified in a new field in the room configuration
dialog, accessible through compatible clients.

Use [language codes](https://en.wikipedia.org/wiki/ISO_639) like `en`,
`fr`, `de` etc.

# Compatibility

Meant for use with Prosody 0.10.x

Native support was [added in Prosody
trunk/0.11](https://hg.prosody.im/trunk/rev/9c90cd2fc4c3), so there is
no need for this module.