Feature/xml memleak fix

[Den271]

PR for XML weak_ptr memory leak fix

1. Started from develop branch, created feature/xml_memleak_fix branch
2. in feature/xml_memleak_fix, Fixed VS2013 compilation errors
3. in feature/xml_memleak_fix, Fixed ReadiumSDK code to be built with SDKLauncher-Win project
4. in feature/xml_memleak_fix, Added the weak_pointer fix
5. Created this Pull Request, base:develop compare:feature/xml_memleak_fix

please see the feature/xml_memleak_fix commit history
Note: it is compiled and tested on Windows&VS2013
I'm not sure it would compile ok for the other platforms, so please fix if required
Thanks

[danielweck]

Reviewed. Looks fine to me, but I am not super-familiar with the logic that tracks XML node allocation, shared pointer, etc. So I guess the best way to test this PR is to open-close-open a number of EPUBs on iOS, Android and / or OSX, and profile / trace memory state. Unfortunately I don't think it is safe to assume that "if it works on platform-A, it should work on platform-B" (because of XML lib + WebView discrepancies?).

[danielweck]

Concern regarding the Windows build files:
https://github.com/readium/readium-sdk/tree/feature/feature_revised_launcher
https://github.com/readium/readium-sdk/tree/feature/feature_revised_launcher_memleakfix
https://github.com/readium/readium-sdk/tree/feature/feature_revised_launcher_memleakfix_64bit_libzip

[danielweck]

Also vcxproj question (which one to use from a launcher app's sln Visual Studio solution, ePub3 or ReadiumSDK?):

https://github.com/readium/readium-sdk/tree/feature/feature_revised_launcher/Platform/Windows

https://github.com/readium/SDKLauncher-Windows/tree/feature/feature_revised_launcher/SDKLauncher-Win

[danielweck]

I commented here about separating the Windows-specific code changes (i.e. the memory leak fix should work in all platforms):
#191 (comment)

[rkwright]

This is part of the work on Windows. As our support for Windows is up in the air, not sure what we will do here.