Add purescript/transformers and purescript/exceptions to enable authors to create custom assertion functions

[hobovsky]

Motivated by this translation.

I wanted to create my own assertion, because basic Spec assertions do not allow for custom messages. I came up with:

-- shouldEqualMsg :: String -> String -> String -> MonadThrow Error Unit
shouldEqualMsg v1 v2 msg = when (v1 /= v2) $ fail msg

However, signatures of assertion functions use types which are not available in packages defined as dependencies accessible for code of kata:

• ModanThrow is provided by the package purescript-transformers,
• Error is provided by the package purescript/exceptions.

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:+1: reaction might help to get this request prioritized.

[kazk]

The container image for PureScript is maintained in https://github.com/codewars/purescript

Can you open a PR?