Log Message:
pugixml: update to 1.11.

pugixml-1.11 is out. This is a maintenance release that fixes some
compatibility issues and introduces several new APIs (read the
changelog for details).

Highlights for this release include:

* Add xml_node::remove_attributes and xml_node::remove_children
* Add a way to customize floating point precision via xml_attribute::set
  and xml_text::set overloads
* XPath parser now limits recursion depth which prevents stack
  overflow on malicious queries