gpclient: adding AutoCloseable to PVReader and PVWriter

Author: gcarcassi

gpclient/gpclient-core/src/main/java/org/epics/gpclient/PVReader.java

@@ -44,7 +44,7 @@
  * @author carcassi
  * @param <T> the type of the PVReader.
  */
-public interface PVReader<T> {
+public interface PVReader<T> extends AutoCloseable {
 
     /**
      * Returns the current value of the PVReader.

gpclient/gpclient-core/src/main/java/org/epics/gpclient/PVWriter.java

@@ -17,7 +17,7 @@
  * @param <T> type of the write payload
  * @author carcassi
  */
-public interface PVWriter<T> {
+public interface PVWriter<T> extends AutoCloseable {
 
     /**
      * Writes a new value asynchronously using the default callback. The result