Remove suspicious instances + some new ones

[expipiplus1]

• Replace Default instance for Diagnostic with Monoid
• Derive Eq and Ord for Marker (Removing the old ones which violated extensionality)
• Add Eq and Ord instances to Note
• Functor, Foldable, Traversable instances for Report, Marker and Note

[expipiplus1]

In anticipation of #21 being merged, I've rebased this on that; the diff should be less intimidating once #21 is merged.

I took the liberty of including #17, the chief objection there seemed to be against unnecessarily tying this package to GHC, however that ship sailed a long time ago, the package already uses a heap of language extensions only supported on GHC. Not to mention that few (none?) of the dependencies will have been tested against any other compiler.

{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE PatternSynonyms #-}

[Mesabloo]

That's absolutely true. I thought depending on GHC's package was a problem, but we already depend on GHC by using language extensions (some of them may be supported by some other Haskell compilers, although I absolutely don't know about that).
I'll merge this a bit later (and publish a new version on hackage).

[expipiplus1]

@Mesabloo any chance of getting a release on Hackage with this + latest changes?

[Mesabloo]

Oh yes absolutely. I completely forgot about that. Sorry!

[Mesabloo]

@expipiplus1 Published as v2.5.1!

[expipiplus1]

Merci beaucoup!