change utf8_encode and utf8_decode

ensure strictly valid UTF-8 output by using utf-8-strict instead of utf8
(see in Encode: 'encode_utf8' and 'UTF-8 vs. utf8 vs. UTF8'
 and in perlunifaq: What's the difference between "UTF-8" and "utf8"?)

Change-Id: I6d8797ddd24339ecf2ab4ccacad3801a6a054ca2
diff --git a/t/data/template.i5.xml b/t/data/template.i5.xml
new file mode 100644
index 0000000..9e0b26d
--- /dev/null
+++ b/t/data/template.i5.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE idsCorpus  PUBLIC "-//IDS//DTD IDS-I5 1.0//EN" "http://corpora.ids-mannheim.de/I5/DTD/i5.dtd">
+<idsCorpus>
+  <idsHeader type="corpus">
+    <fileDesc>
+      <titleStmt>
+        <korpusSigle>[KORPUSSIGLE]</korpusSigle>
+      </titleStmt>
+    </fileDesc>
+  </idsHeader>
+  <idsDoc version="1.0">
+    <idsHeader type="document">
+      <fileDesc>
+        <titleStmt>
+          <dokumentSigle>[DOKUMENTSIGLE]</dokumentSigle>
+        </titleStmt>
+      </fileDesc>
+    </idsHeader>
+    <idsText version="1.0">
+      <idsHeader type="text">
+        <fileDesc>
+          <titleStmt>
+            <textSigle>[TEXTSIGLE]</textSigle>
+          </titleStmt>
+        </fileDesc>
+      </idsHeader>
+      <text>
+        [TEXT]
+      </text>
+    </idsText>
+  </idsDoc>
+</idsCorpus>