Move the German addons to gobl.de.xinvoice

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 
 ### Changed
 
+- `addons`: the German `de-xrechnung-v3` and `de-zugferd-v2` addons move out of core into [`github.com/invopop/gobl.de.xinvoice`](https://github.com/invopop/gobl.de.xinvoice) and join the approved external addon list. As with the other external addons, the module must be imported (`_ "github.com/invopop/gobl.de.xinvoice/addon/xrechnung"` and `_ "github.com/invopop/gobl.de.xinvoice/addon/zugferd"`) for documents declaring those keys to calculate and validate; `gobl.dev/bundle` does this for the services that use it. The German examples and the generated addon and rule data move with them.
 - `net`: spec §5.3 — a party re-countersigning an envelope MUST replace its own earlier countersignatures (supersession); removing another party's signatures remains forbidden. In steady state an endorsed identity carries exactly three signatures: the subject's, the Authority's, and the verifier's.
 
 ### Added

addons/addons.go

@@ -11,8 +11,6 @@ import (
 	// Import all the addons to ensure they're ready to use.
 	_ "github.com/invopop/gobl/addons/ar/arca"
 	_ "github.com/invopop/gobl/addons/co/dian"
-	_ "github.com/invopop/gobl/addons/de/xrechnung"
-	_ "github.com/invopop/gobl/addons/de/zugferd"
 	_ "github.com/invopop/gobl/addons/es/facturae"
 	_ "github.com/invopop/gobl/addons/es/sii"
 	_ "github.com/invopop/gobl/addons/es/tbai"