Markdown support in the @deprecated message.

[naomieow]

Markdown support in the @deprecated message for when it generates in the documentation. This would allow something like this:

/// Set the auth token for authentication - this is in a query
@deprecated("This authentication option is deprecated for removal in Gitea 1.23. use [`with_auth_header_token`](#with_auth_header_token) instead.")
pub fn with_auth_token(settings: Settings, token token: String) -> Settings {
  Settings(..settings, token: Some(token))
}

[lpil]

How would this work given that this message is also included in the command line, in the language server, etc?