* Add a test for scatter add (segfaults on gpus for now). * Bugfix for the scatter add cuda kernel.
* Skeleton methods for IndexAdd/ScatterAdd. * Add a Map2InPlace trait. * Add the glue code for the index-add/scatter-add kernels. * Tweak the file name: embeddings -> indexing. * Add the cuda kernel for indexadd. * And add the scatter-add kernels.