Support noValidation option from xmlbuilder1

[kellyselden]

I'm transforming an XML (JUnit) file, and it would be nice if the attributes matched. Right now this is what happens:

input:

<testsuite>
  <testcase name="foo > bar"/>
</testsuite>

output:

<testsuite>
  <testcase name="foo &gt; bar">
    <failure/>
  </testcase>
</testsuite>

I understand that the output is more correct, but it would be nice to match the option from xmlbuilder1 noValidation https://github.com/oozcitak/xmlbuilder-js/blob/e4ddc615b3668c63c63e627fb1b6fc078d586ba3/src/XMLStringifier.coffee#L164.

[oozcitak]

The library applies the XMLSerializer interface as is. I want to keep the default implementation as close to the specs as possible. The option you require will be possible with custom serializers. Please watch the related issue: #47.