Add preliminary support for split into annual volumes

and drop support for not splitting

e.g. `make test YY=18`

does not yet work for the index
diff --git a/xslt/idsCorpus-template.xml b/xslt/idsCorpus-template.xml
index 80608a2..4d042cb 100644
--- a/xslt/idsCorpus-template.xml
+++ b/xslt/idsCorpus-template.xml
@@ -4,7 +4,7 @@
   <idsHeader TEIform="teiHeader" pattern="allesaußerZtg/Zschr" status="new" type="corpus" version="1.1">
     <fileDesc>
       <titleStmt>
-        <korpusSigle>DNB</korpusSigle>
+        <korpusSigle>DNB{YY}</korpusSigle>
         <c.title>Deutsche Nationalbibliothek: Belletristik</c.title>
       </titleStmt>
       <publicationStmt>