Changed parser to xmlbuilder2

What's new ?

Internals

XML parser/serializer library changed from xmldom to xmlbuilder2.

• xmldom was source of issue #59, and has no options for fixing that issue.
• xmlbuilder2 is faster than xmldom, is maintained better and is successor of extremely popular xmlbuilder package. Also, it is more standard compliant

Breaking changes

There are no breaking changes in both package api and cli, however:

• xml parser switch may affect contents of combined xml
• xmlbuilder2 does not support xml version 1.1, so junit-report-merger won't be able to process xml files with version 1.1 anymore. To my knowledge no tools use xml version 1.1 in their test reports, so this should not affect people.