Bump base upper bound

Bump base upper bound to 4.15

This fixes a handful of minor issues with the `NFData` instance for
`URec`:

* It had a `@since` annotation without Haddock formatting.
* It did not mention that it was only available on `base-4.9` or
  later.
* The CPP referred to `__GLASGOW_HASKELL__`, not
  `MIN_VERSION_base(4,9,0)` like it should have.

This patch fixes all of these problems.

...for the TypeRep/TypeCon instances

See https://ghc.haskell.org/trac/ghc/ticket/15018.

With the recent new API additions it makes sense to restructure
a bit. Moreoever, this commit augments the new NFData1/NFData2 API
with a few more haddock strings, and extends the introductory examples.

[skip ci]

This makes sure that the compiler has a better chance to warn/complain if
we forget to update the BackDoor module when `base` changes

...this required to update C.D.BackDoor

This was made necessary by #28

This hack reduces the surface-area requiring TRUSTWORTHY annotations

...and add GHC 8.2.1 to CI matrix

Plus some minor code cleanup

Oleg Grenrus authored 8 years ago and Ryan Scott committed 8 years ago

* Add NFData1 and NFData2 classes

* Add Changelog entries

* Add Changelog for NFData1/2

* Generate tuple instances for NFData1/2

* Add NFData1 Fixed and Ratio

* Generic NFData1

* Add NFData1 generic deriving docs

* Add |@since 1.4.3.0

* Add NFData1/2 Array instances

* *Var/*Ptr NFData1 instances