Add support for JSON in H2 using circe

[andrzejressel]

This PR introduces support for JSON type in H2.

Code and tests are based on Postgres implementation.

I've tried using native H2 type ValueJson, but H2 really insists on using VARCHAR/bytearray:

    implicit val jsonPut: Put[Json] =
      Put.Advanced.other[ValueJson](
        NonEmptyList.of("JSON", "json")
      ).tcontramap(a =>
        ValueJson.fromJson(a.noSpaces)
      )
	  
	implicit val jsonGet: Get[Json] =
      Get.Advanced.other[ValueJson](
        NonEmptyList.of("JSON", "json")
      ).temap(a =>
        parse(a.getString).leftMap(_.show)
      )

[jatcwang]

Do you mean

Suggested change

	import doobie.h2.circe.json.implicits
	import doobie.h2.circe.json.implicits._

?

Also wondering whether we should mention that instances need to be created explicitly with h2DecoderGetT h2EncoderGetT?

[andrzejressel]

To be honest I was thinking about adding ._, but I haven't saw that in PostgreSQL implementation that I based my code on.

Regarding h2DecoderGetT and h2EncoderGetT, from what I understand they're used mostly for testing.

[jatcwang]

Regarding h2DecoderGetT and h2EncoderGetT, from what I understand they're used mostly for testing.

They are used for creating instances of Put[A]/Get[A] provided that you have Encoder[A]/Decoder[A]. This isn't automatically derived (i.e. not implicit def) because that can often lead to the wrong behaviour. (Just because you have an Encoder[A] does not mean you want to write A as a JSON column in the database).

Anyway I can do the doc improvements in another PR. Thanks for your contribution :)