Add notes/symlinks.md documenting required symbolic links for the appinstaller and shared directories, plus guidance for creating symlinks in Debug/Release and including shared subdirs in releases. Update pkgread project and its filters to use a relative path for pugixml.cpp (..\packages\pugixml.1.15.0\...) instead of an absolute user-specific NuGet path so the project is portable and includes pugixml.cpp needed to resolve linker errors for non-x86 builds (e.g. ARM).
Upgrade solution to Visual Studio 17 and add ARM build configurations across projects. Several .vcxproj files were updated to include Debug/Release|ARM property groups, property sheet imports and LinkIncremental settings; platform toolset set for ARM configs where appropriate. A new pugixml_arm project and its sources/filters were added. Also added ExtensibilityGlobals (SolutionGuid) to the .sln.
