Free Applicative

[pakoito]

I need to start a discussion before continuing with the implementation, as cats has recently done a refactor-overhaul themselves. The new version is stack-safe, performs better, and reads worse than anything else in our repo.

Reasoning for refactor: typelevel/cats#1151 (comment)

PR: typelevel/cats#1748

Implementation: typelevel/cats@693f456#diff-19bafa82f16b79d5e02c62e0d1612d28R39

The scalaz counterpart: https://github.com/scalaz/scalaz/blob/series/7.3.x/core/src/main/scala/scalaz/FreeAp.scala

[raulraja]

I think that if the new version by Edmund in Scala is stack-safe that is more important than the implementation readability and ours should resemble that one instead of the previous one. Kategory is a general purpose library that is ment to serve as companion to the stdlib stack-safety and performance is a concern most of our users are going to care and impure and dirty impls to achieve that is a fair trade-off because : FP in the JVM xD