Split out HKernel.

[milessabin]

[vil1]

@milessabin is this issue still active ?

If so, can you specify what you mean by "split out"? Is the purpose of that issue to extract HKernel* from its current location in shapeless/ops/hlists.scala and make it a first-class citizen (eg in a shapeless/hkernel.scala file), potentially with its own ops/syntax? Or is it something broader than that?

[joroKr21]

Shapeless 3 is here: https://github.com/typelevel/shapeless-3