Feature/xsltfixes

Hi!

I have added some features to the xml based functionality such that it is actually useable.
See the unit tests for use cases:
- Attribute_values_can_be_extracted
- No_need_to_convert_node_contents_to_text
- Xpath_can_use_doc_namespaces
- Xpath_uses_doc_default_namespace
- Xpath_processor_is_version_2
It also builds with recent atlas-mvn, and the repo can be compiled with drone.io, see https://drone.io/github.com/magwas/andreymarkelov-atlas-plugins-requestedfields

Please incorporate it to your upstream.
If anything should be changed for inclusion, please let me know.