Migrate from TinyXML v1 to v2. Not bundled (yet).
Suppress some annoying warnings about offsetof.
Include tinyxml2, update cmake to use this optionally
vcproj update
Merge branch 'tinyxml2' into experimental. Thanks to James Le Cuirot for this.

Conflicts:
	Aquaria/UserSettings.cpp
	CMakeLists.txt
Fixes to prev commit - restore ttvfs functionality when reading XML files, and minor other things
Disable tinyxml2's LoadFile() functions to catch ttvfs bypass for reading