common groupBy variants

[cvogt]

Seq[(A,B)].groupBy(_._1,_._2): Seq[(A, Seq[B])] /*or*/ Seq[(A,B)].groupBy(e => e._1 -> e._2): Seq[(A, Seq[B])]
Seq[(A,B)].groupByLeft: Map[A,Seq[B]]
Seq[(A,B)].groupByRight: Map[B,Seq[A]]