Added MultiMap.merge, closes #108
Generalized List[(K, V)].toMultiMap to FilterMonadic[(K, V), Repr].toMultiMap
Generalized asMultiMap, asMap, etc to GenTraversableLike, closes #107

asMap, asMultiMap, as[F[_, _]], attributeCounts, collectAttributeCounts,
optAttributeCounts
Merge branch 'master' into 2.9

Conflicts:
	core/src/main/scala/pimpathon/list.scala
	core/src/main/scala/pimpathon/set.scala