Referer - returned from parse, a sealed hierarchy which can be an
UnknownReferer, SearchReferer, InternalReferer, SocialReferer, EmailReferer,
or PaidReferer.
final case classRefererLookup(medium: Medium, source: String, parameters: List[String]) extends Product with Serializable
final case classSearchReferer(medium: Medium, source: String, term: Option[String]) extends Referer with Product with Serializable
final case classSocialReferer(medium: Medium, source: String) extends Referer with Product with Serializable