add instance Traversable UrlMap'

[chris-martin]

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• Bumped the version number
• Documented new APIs with Haddock markup
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[Vlix]

This looks fine, not a big change or anything.

If you could merge in master so that all the CI works again, we can probably merge this in 🤔

[kazu-yamamoto]

@chris-martin Could you rebase and push -f this branch again?