xml2 1.3.3

• Hadley Wickham is now (again) the maintainer.

• xml2 has been re-licensed as MIT (#317).

• xml_find_all.xml_node() fails more informatively the xpath parameter is the wrong type (@MichaelChirico)

• xml_find_all.xml_nodeset() gains a flatten argument to control whether to return a single nodeset or a list of nodesets (#311, @jakejh)

• write_xml() and write_html() now return NULL invisibly, as they did prior to version 1.3.0 (#307)

• XPtr gets explicit copy constructor and assignment operator definitions, which were two missing components of the Rule of three (@MichaelChirico)

• Windows: update to libxml2 2.9.10 and libxslt 1.1.34 and add ucrt libs