Make ProtoDeserializer and ProtoSerializer public

fixes #706

Author: Tim Aebi

formats/protobuf/src/main/java/io/cloudevents/protobuf/ProtoDeserializer.java

@@ -34,7 +34,7 @@
 /**
  * Implements a {@link CloudEventReader} that can deserialize a {@link CloudEvent} protobuf representation;
  */
-class ProtoDeserializer implements CloudEventReader {
+public class ProtoDeserializer implements CloudEventReader {
     private final CloudEvent protoCe;
 
     public ProtoDeserializer(CloudEvent protoCe) {

formats/protobuf/src/main/java/io/cloudevents/protobuf/ProtoSerializer.java

@@ -45,7 +45,7 @@
 /**
  * Provides functionality for turning a {@link io.cloudevents.CloudEvent} to the protobuf representation {@link CloudEvent}.
  */
-class ProtoSerializer {
+public class ProtoSerializer {
 
     /**
      * Convert the Java SDK CloudEvent into a protobuf representation.