Add XML payload support

Fixes #238

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

@@ -0,0 +1,20 @@
+package mxj
+
+// Per: https://github.com/clbanning/mxj/issues/37#issuecomment-278651862
+var fieldSep string = ":"
+
+// SetFieldSeparator changes the default field separator, ":", for the
+// newVal argument in mv.UpdateValuesForPath and the optional 'subkey' arguments
+// in mv.ValuesForKey and mv.ValuesForPath. 
+// 
+// E.g., if the newVal value is "http://blah/blah", setting the field separator
+// to "|" will allow the newVal specification, "<key>|http://blah/blah" to parse
+// properly.  If called with no argument or an empty string value, the field
+// separator is set to the default, ":".
+func SetFieldSeparator(s ...string) {
+	if len(s) == 0 || s[0] == "" {
+		fieldSep = ":" // the default
+		return
+	}
+	fieldSep = s[0]
+}