A functor provides the map operation that allows lifting an f
function into the functor context and applying it.
To implement Functor:
The purpose of this type-class is to support the data-types in the
Monix library and it is considered a shim for a lawful type-class
to be supplied by libraries such as Cats or Scalaz or equivalent.
CREDITS: The type-class encoding has been inspired by the Scato
project by Aloïs Cochard and Scalaz 8
and the type has been extracted from Cats.