fs2-kafka v0.19.4

Additions

• Add improved support for unkeyed records. Thanks @ranjanibrickx! (#96, #97)
  • Add Deserializer#option, and Deserializer.option and unit.
  • Add HeaderDeserializer#option, and HeaderDeserializer.option and unit.
  • Add Serializer#option, and Serializer.option, asNull, empty and unit.
  • Add HeaderSerializer#option, and HeaderSerializer.option, asNull, empty and unit.

Released on 2019-03-01.