Reduce visibility of classes/interfaces where possible

Author: sungshik

src/main/java/engineering/swat/watch/impl/mac/NativeEventHandler.java

@@ -50,6 +50,6 @@
  * </p>
  */
 @FunctionalInterface
-public interface NativeEventHandler {
+interface NativeEventHandler {
     <T> void handle(Kind<T> kind, @Nullable T context);
 }

src/main/java/engineering/swat/watch/impl/mac/NativeEventStream.java

@@ -75,7 +75,7 @@
  * these methods are expected to be rarely invoked.
  * </p>
  */
-public class NativeEventStream implements Closeable {
+class NativeEventStream implements Closeable {
 
     // Native APIs
     private static final CoreFoundation   CF  = CoreFoundation.INSTANCE;