* Add grouping to scaladoc for arity methods

This makes it so when you look at the `Applicative` scaladoc you don't
have a bunch of `ap3`, `ap4`, etc noise mixed in with the more
meaningful methods. Instead, the generated higher-arity methods show up
in separate scaladoc groups below.

To see the changes you can pull this branch, run `sbt unidoc` (you may
need to clean first), and open
`cats/docs/target/scala-2.12/unidoc/cats/Applicative.html` in your
browser.

* Add doctest examples for Apply (#2086)

* Get ready for RC2 (#2044)

* Draft release notes

* Update

* Update

* Update

* Update

* Update

* Update Authors

* Update

* Update

* Update

* Update

* update

* Update

* Update CHANGES.md

* Update AUTHORS.md

* Update README.md

* Update deprecations to product{L,R} instead of ap{L,R}