Remove contrib folder

This change removes contrib folder since it doesn't seem very useful;
Natvis scripts can and should go to scripts/ along with project files.

foreach.hpp is supporting a severely outdated BOOST_FOREACH construct;
in C++11 ranged for loop can be used with xml_node::children/attributes,
and BOOST_FOREACH can work with these as well.

foreach.hpp was also accidentally licensed as public domain which isn't
very helpful when the actual library is MIT. We could fix the license
but it seems better to just remove it.

Fixes #264.

contrib/foreach.hpp

-/*
- * Boost.Foreach support for pugixml classes.
- * This file is provided to the public domain.
- * Written by Arseny Kapoulkine (arseny.kapoulkine@gmail.com)
- */
-
-#ifndef HEADER_PUGIXML_FOREACH_HPP
-#define HEADER_PUGIXML_FOREACH_HPP
-
-#include <boost/range/iterator.hpp>
-
-#include "pugixml.hpp"
-
-/*
- * These types add support for BOOST_FOREACH macro to xml_node and xml_document classes (child iteration only).
- * Example usage:
- * BOOST_FOREACH(xml_node n, doc) {}
- */
-
-namespace boost
-{
-	template<> struct range_mutable_iterator<pugi::xml_node>
-	{
-		typedef pugi::xml_node::iterator type;
-	};
-
-	template<> struct range_const_iterator<pugi::xml_node>
-	{
-		typedef pugi::xml_node::iterator type;
-	};
-
-	template<> struct range_mutable_iterator<pugi::xml_document>
-	{
-		typedef pugi::xml_document::iterator type;
-	};
-
-	template<> struct range_const_iterator<pugi::xml_document>
-	{
-		typedef pugi::xml_document::iterator type;
-	};
-}
-
-/*
- * These types add support for BOOST_FOREACH macro to xml_node and xml_document classes (child/attribute iteration).
- * Example usage:
- * BOOST_FOREACH(xml_node n, children(doc)) {}
- * BOOST_FOREACH(xml_node n, attributes(doc)) {}
- */
-
-namespace pugi
-{
-	inline xml_object_range<xml_node_iterator> children(const pugi::xml_node& node)
-	{
-		return node.children();
-	}
-
-	inline xml_object_range<xml_attribute_iterator> attributes(const pugi::xml_node& node)
-	{
-		return node.attributes();
-	}
-}
-
-#endif