publishing pojo as avro

[adyach]

with this commit it is easy to use Avro as never:

1. update library dependencies
2. in Nakadi client builder provide Avro serializer:

    final NakadiClient client = NakadiClient.newBuilder()
        ...
        .serializationSupport(AvroSerializationSupport.newInstance())
        .build();

the pojo business / data change events will be serialized to Avro.