Semigroups, Monoids, Zips, and AsRecord

[parsonsmatt]

This PR introduces Prairie.Semigroup, allowing you to appendRecord :: (Record rec, FieldDict Semigroup rec) => rec -> rec -> rec. We also get Prairie.Monoid, giving you emptyRecord :: (Record rec, FieldDict Monoid rec) => rec. These are pretty self-explanatory.

appendRecord is implemented with zipWithRecord :: (Record rec) => (forall ty. ty -> ty -> Field rec ty -> ty) -> rec -> rec -> rec, also introduced here. This allows you to combine two records with a function specifying how to combine the values.

Finally, we provide AsRecord, a newtype for DerivingVia which lets you derive Monoid and Semigroup instances using the behavior of appendRecord and emptyRecord.

Before submitting your PR, check that you've:

• Bumped the version number.
• Documented new APIs with Haddock markup.
• Added @since declarations to the Haddock.
• Ran stylish-haskell and otherwise adhered to the style guide.

After submitting your PR:

• Update the Changelog.md file with a link to your PR.
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts).

[evanrelf]

Sick