Escape text values in OutputXML

[MrBeldum]

OutputXML writes JSON string values into the XML as-is. Any value that contains <, > or & therefore produces output that isn't well-formed XML:

doc, _ := jsonquery.Parse(strings.NewReader(`{"a": "AT&T", "b": "<i>"}`))
fmt.Println(doc.OutputXML())
// before: <?xml version="1.0" encoding="utf-8"?><root><a>AT&T</a><b><i></b></root>
// after:  <?xml version="1.0" encoding="utf-8"?><root><a>AT&amp;T</a><b>&lt;i&gt;</b></root>

encoding/xml rejects the old output (XML syntax error ... expected attribute name in element).

Change: text nodes now go through a small strings.Replacer that escapes &, < and >. Element names and InnerText() are not touched.

Test: TestOutputXMLEscapesText compares the exact output and checks that xml.Unmarshal decodes it back to the original strings. The test fails without the change and passes with it. go test ./... passes.