core: 
effect: 
Sequential computation over parallel computation
It's a simplified tool for building pure FP programs in scala.
It comes from Freestyle, but Freestyle is complicated, I only need some basic
elements for building pure functional programs.
Par is the abstraction of parallel
We should add a sbt plugin of partial-unification to avoid SI-2712:
addSbtPlugin("org.lyranthe.sbt" % "partial-unification" % "1.0.0")
@Millesabin has fix it in 2.12: scala/scala#5102