Merge pull request #3 from JonnyH/linux

Linux support & resource datafile loading abstraction
Build fixes
Migrating to VS2013
Some tweaking
Resources

Load individual image from PCK
Start of form class
Import of tinyxml2
Create License
Rename License to LICENSE
Start of UI code

And renaming all std::string to std::wstring
Revert from wstring (need to work out how to properly support unicode)
Some UI controls
Form events
Text Buttons (almost graphically equal to original, but sizable)
Texture on Text button, and drop shadows in menu
GraphicButton control
Add form files to cmake build
Fix gcc build - can't convert a nullptr to XMLDocument
Merge pull request #4 from JonnyH/master

Fix linux build after forms work
New GameCore system
Loading from XML - but having trouble with cache maps
Fixed map bug.