-registering same system multiple times only replace pointer for callback

-added export attributes (required by windows to make DLL library, not work at now due to DMD bugs)
-interface D files to import

dub.json

@@ -16,6 +16,18 @@
 			"name" : "tests",
 			"sourcePaths" : ["source\/","tests\/"],
 			"targetType" : "executable"
+		},
+		{
+			"name" : "dynlib",
+			"targetType" : "dynamicLibrary"
+		},
+		{
+			"name" : "sources",
+			"targetType" : "dynamicLibrary",
+			"dflags": [
+				"-Hdimport/",
+				"-op"
+			]
 		}
 	]
 }