Add Dispatcher header to EnTT global include (#59)

Add dispatcher.hpp to entt.hpp

src/entt/entt.hpp

@@ -14,6 +14,7 @@
 #include "resource/loader.hpp"
 #include "signal/bus.hpp"
 #include "signal/delegate.hpp"
+#include "signal/dispatcher.hpp"
 #include "signal/emitter.hpp"
 #include "signal/sigh.hpp"
 #include "signal/signal.hpp"