Derive Show instances for route data structures

[MaxGabriel]

• It's very helpful to have a Show instance for debugging and development
• Currently third party packages are deriving this instance themselves which is not ideal.
  • http://hackage.haskell.org/package/yesod-routes-flow-2.0/docs/src/Yesod-Routes-Flow-Generator.html
  • http://hackage.haskell.org/package/yesod-routes-typescript-0.3.0.0/docs/src/Yesod-Routes-Typescript-Generator.html
  • This change would break those packages, which isn't great
    • At least the typescript one is broken anyway

I haven't looked into this much, but if someone knows offhand, what is the use case for Piece and Dispatch being parametrized data types? It seems like they would most always be String?

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[MaxGabriel]

Since yesod-routes-flow is being actively developed, I think a good solution is to have a preprocessor macro that says that if yesod-core is >= this version, then don't derive the show instances.

Edit: created a PR freckle/yesod-routes-flow#4

[MaxGabriel]

Honestly seems like I should also basic typeclasses like Eq and Ord as well.

[snoyberg]

LGTM!