Automate creating subprojects for different versions of compiler

[DmytroMitin]

https://github.com/ghik/sbt-nosbt

(https://github.com/sbt/sbt-pom-reader)

or macro annotation

or

import sbt._
import Keys._

object BuildImpl extends AutoPlugin {
  override def extraProjects: Seq[Project] = (0 to 10).map(i => {
    val name = s"proj2_13_$i"
    Project(name, file(name))
      .settings(scalaVersion := s"2.13.$i")
  })
}