use sbt-boilerplate for generating stubs
(cherry picked from commit b4b2208d045fd7ee1549f56c2b9d897c5caceb48)

This allows to have jsonFormat for more than 15 case class parameters. Fixes #48

Conflicts:
	build.sbt
	project/plugins.sbt
	src/main/boilerplate/cc/spray/json/ProductFormatsInstances.scala.template