Play-Json extensions

This is a minimal fork of bizzabo/play-json-extensions.

This fork is restricted in the versions it supports:

• Scala 2.13 (some of this library may eventually be available for Scala 3)
• play-json 3.0.x, specifically only for the org.playframework group id, not com.typesafe.play (see guardian/maintaining-scala-projects#4 for the bad consequences of mixing)

Difference from bizzabo/play-json-extensions

The fork was taken at commit ec3a07e5. It has some modifications:

• Modifications to compile on later versions of Scala 2.13
• Maven Group id: ai.x → com.gu
• Class package: ai.x.play.json → com.gu.ai.x.play.json