Separate NAZARA_API into multiple defines (one per module)

To fix inter-module dependency


Former-commit-id: 64704f020e0af22e529d38527323ba977187d4d0

include/Nazara/Core/StringStream.hpp

@@ -12,7 +12,7 @@
 #include <string>
 #include <vector>
 
-class NAZARA_API NzStringStream
+class NAZARA_CORE_API NzStringStream
 {
 	public:
 		NzStringStream();