Add XML payload support

Fixes #238

vendor/github.com/clbanning/mxj/escapechars.go

@@ -0,0 +1,54 @@
+// Copyright 2016 Charles Banning. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file
+
+package mxj
+
+import (
+	"bytes"
+)
+
+var xmlEscapeChars bool
+
+// XMLEscapeChars(true) forces escaping invalid characters in attribute and element values.
+// NOTE: this is brute force with NO interrogation of '&' being escaped already; if it is
+// then '&' will be re-escaped as '&'.
+//  
+/*
+	The values are:
+	"   "
+	'   '
+	<   &lt;
+	>   &gt;
+	&   &amp;
+*/
+func XMLEscapeChars(b bool) {
+	xmlEscapeChars = b
+}
+
+// Scan for '&' first, since 's' may contain "&amp;" that is parsed to "&amp;amp;" 
+// - or "&lt;" that is parsed to "&amp;lt;".
+var escapechars = [][2][]byte{
+	{[]byte(`&`), []byte(`&amp;`)},
+	{[]byte(`<`), []byte(`&lt;`)},
+	{[]byte(`>`), []byte(`&gt;`)},
+	{[]byte(`"`), []byte(`&quot;`)},
+	{[]byte(`'`), []byte(`&apos;`)},
+}
+
+func escapeChars(s string) string {
+	if len(s) == 0 {
+		return s
+	}
+
+	b := []byte(s)
+	for _, v := range escapechars {
+		n := bytes.Count(b, v[0])
+		if n == 0 {
+			continue
+		}
+		b = bytes.Replace(b, v[0], v[1], n)
+	}
+	return string(b)
+}
+