Add public support for SpanDecorators (#78)

Changes the visibility for `buildAndFinishChildSpan` and `buildAndInjectSpan` to be public for all methods so that a custom list of SpanDecorators can be provided. This is necessary when outside the `TracingKafkaConsumer` and `TracingKafkaProducer`. An example would be custom tracing interceptors for use with kafka connect.

opentracing-kafka-client/src/main/java/io/opentracing/contrib/kafka/TracingKafkaUtils.java

@@ -68,7 +68,7 @@ public static <K, V> Span buildAndInjectSpan(ProducerRecord<K, V> record, Tracer
         Collections.singletonList(SpanDecorator.STANDARD_TAGS));
   }
 
-  static <K, V> Span buildAndInjectSpan(ProducerRecord<K, V> record, Tracer tracer,
+  public static <K, V> Span buildAndInjectSpan(ProducerRecord<K, V> record, Tracer tracer,
       BiFunction<String, ProducerRecord, String> producerSpanNameProvider,
       SpanContext parent, Collection<SpanDecorator> spanDecorators) {
     String producerOper =
@@ -112,7 +112,7 @@ public static <K, V> void buildAndFinishChildSpan(ConsumerRecord<K, V> record, T
         Collections.singletonList(SpanDecorator.STANDARD_TAGS));
   }
 
-  static <K, V> void buildAndFinishChildSpan(ConsumerRecord<K, V> record, Tracer tracer,
+  public static <K, V> void buildAndFinishChildSpan(ConsumerRecord<K, V> record, Tracer tracer,
       BiFunction<String, ConsumerRecord, String> consumerSpanNameProvider,
       Collection<SpanDecorator> spanDecorators) {
     SpanContext parentContext = TracingKafkaUtils.extractSpanContext(record.headers(), tracer);