Using Kafka style SerDes

[matzew]

@ppatierno here we go w/ the SerDes approach, discussed in #4

[matzew]

Besides my committed changes, I get auto changes on .adoc file, and some Kotlin code is generated:

On branch KafkaSerDes
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   src/main/asciidoc/java/index.adoc

Untracked files:
  (use "git add <file>..." to include in what will be committed)

	src/main/kotlin/io/vertx/kotlin/kafka/client/consumer/OffsetAndTimestamp.kt

no changes added to commit (use "git add" and/or "git commit -a")

Feels a bit odd :)