* Allow a singular entity to be returned from an update
Since a `PATCH` will be an update that could affect many rows, there might be
more than one object returned. By allowing asking for a singular response,
the/an object will be returned instead of a list. This is useful in cases when
the `PATCH` is against single entity (i.e. `/items?pkey=eq.99`).
* Add tests for plurality=singular for `PATCH` requests
* Disallow updating more than one row if `plurality=singular`
As discussed in #634, we don't want to allow updating several rows with
a `PATCH` request when the `Prefer` header specifies
`return=representation;plurality=singular` as this would almost
certainly be a client error.
* Add test for patching multiple objects with singular response
Patching > 1 object with `return=representation;plurality=singular`
should return `400 Bad Request`.
* Only add singleton range for read API requests
* Disallow inserting more than one row if `plurality=singular`
Disallow inserting several rows with a `POST` request when the `Prefer`
header specifies `return=representation;plurality=singular` as this
would almost certainly be a client error.
* Only import `q` from `Text.InterpolatedString.Perl6`
* Update OpenAPI response for PATCH/POST to mention `plurality=singular`
The OpenAPI response for PATCH/POST requests now includes the `Prefer` value
`return=representation;plurality=singular`.
* Add entry in changelog
