Add generic container reductions (#62)

* add recursive container reductions

* extend reductions to array containers

* make rec_reduce_array_container more specific

* rename make_container to process_container

* rename rec_reduce_container to rec_map_reduce_container

* fix typo in comment

Co-authored-by: Andreas Klöckner <inform@tiker.net>

Co-authored-by: Andreas Klöckner <inform@tiker.net>