Some header fixes

Samples/basic/sdl2/src/RenderInterfaceSDL2.cpp

@@ -26,7 +26,7 @@
  *
  */
 
-#include <RmlUi/Core/Core.h>
+#include <RmlUi/Core.h>
 #include <SDL_image.h>
 
 #include "RenderInterfaceSDL2.h"

Samples/basic/sfml2/src/RenderInterfaceSFML.cpp

@@ -26,7 +26,7 @@
  *
  */
 
-#include <RmlUi/Core/Core.h>
+#include <RmlUi/Core.h>
 #include "RenderInterfaceSFML.h"
 
 #ifndef GL_CLAMP_TO_EDGE

Source/Core/Template.cpp

@@ -30,6 +30,7 @@
 #include "XMLParseTools.h"
 #include "../../Include/RmlUi/Core/ElementUtilities.h"
 #include "../../Include/RmlUi/Core/XMLParser.h"
+#include <string.h>
 
 namespace Rml {
 namespace Core {

Source/Core/XMLNodeHandlerHead.cpp

@@ -29,7 +29,7 @@
 #include "XMLNodeHandlerHead.h"
 #include "DocumentHeader.h"
 #include "TemplateCache.h"
-#include "../../../Include/RmlUi/Core/Core.h"
+#include "../../Include/RmlUi/Core/Core.h"
 #include "../../Include/RmlUi/Core/Element.h"
 #include "../../Include/RmlUi/Core/ElementDocument.h"
 #include "../../Include/RmlUi/Core/StringUtilities.h"