Pick authors only from dc:creator fields that contain [Verfasser] or nothing in brackets

Resolves #12
diff --git a/xslt/epub2i5.xsl b/xslt/epub2i5.xsl
index 3098242..420dc0d 100644
--- a/xslt/epub2i5.xsl
+++ b/xslt/epub2i5.xsl
@@ -23,7 +23,7 @@
     </xsl:variable>
 
     <xsl:variable name="autor"
-        select="replace(string-join($dnbBookdata//dc:creator[not(matches(., '\[(Erzähler)\]'))], ' ; '), ' *\[[^\]]*\]', '')"/>
+        select="replace(string-join($dnbBookdata//dc:creator[not(contains(., '[')) or matches(., '\[Verfasser\]')], ' ; '), ' *\[[^\]]*\]', '')"/>
 
     <xsl:variable name="straight_autor" select="normalize-space(replace(hlu:reversedAuthors($autor), ',', ''))"/>