Rework enum usage; other refactoring; add getters to HeaderNames.

Author: garyrussell

spring-kafka-docs/src/main/asciidoc/kafka.adoc

@@ -5737,19 +5737,18 @@ The reason for the two properties is because, while you might want to retain onl
 `appendOriginalHeaders` is applied to all headers named `*ORIGINAL*` while `stripPreviousExceptionHeaders` is applied to all headers named `*EXCEPTION*`.
 
 Starting with version 2.8.4, you now can control which of the standard headers will be added to the output record.
+See the `enum HeadersToAdd` for the names of the (currently) 10 standard headers that are added by default.
 
-There is a new property `whichHeaders`, which is a `BitSet`; for example, to suppress the addition of adding the stack trace header, use the following:
+To exclude headers, use the `excludeHeaders()` method; for example, to suppress adding the exception stack trace in a header, use:
 
 ====
 [source, java]
 ----
 DeadLetterPublishingRecoverer recoverer = new DeadLetterPublishingRecoverer(template);
-recoverer.getWhichHeaders().clear(HeaderNames.HeadersToAdd.EX_STACKTRACE.getBit());
+recoverer.excludeHeaders(HeaderNames.HeadersToAdd.EX_STACKTRACE);
 ----
 ====
 
-See the `enum HeadersToAdd` for the bit names of the (currently) 10 standard headers that are added by default.
-
 In addition, you can completely customize the addition of exception headers by adding an `ExceptionHeadersCreator`; this also disables all standard exception headers.
 
 ====