Support older GHC

[viercc]

Matchable, Bimatchable classes themselves can be defined in Haskell98. Currently it requires base >= 4.10.

[viercc]

• Matchable

  • Eq1 exists for ghc >= 8.0 (base-4.9)
    • ghc >= 1.0 using transformers
  • Generics exists since ghc >= 7.2 (base-4.4)

• Bimatchable

  • Eq2 exists for ghc >= 8.0 (base-4.9)
  • Bifunctor exists for ghc >= 7.10
    • Can go older using bifunctors

[viercc]

7acce99 relaxes lower bound to base >=4.9
in excange for intorduction of some orphan instances for containers types (Data.*.Orphans)

[viercc]

5fbfeb7 spits out Data.*.Orphans to separate package

[viercc]

It will be better to depend on functor-classes-compat. See haskellari/functor-classes-compat#8

[viercc]

After more than a year, supporting older (<= 8.0) ghc does not seems to be necessary. Revert all changes aimed to expand compatibility.