XCCDF XML Validation via XSD

Provide the ability to validate an XCCDF XML file content via appropriate XSD.

Possible `npm` packages are:

1. [libxmljs](https://github.com/libxmljs/libxmljs) - Best choice thus far
2. [fast-xml-parser](https://github.com/NaturalIntelligence/fast-xml-parser) - It looks like it doesn't validate using XSD