Use for neural networks (ANN)

Just a heads-up: There's recently been some discussion on reusing arrayfire-js as the back-end in the
[BrainJS](https://github.com/harthur/brain) and [Synaptic](https://github.com/cazala/synaptic) frameworks:

https://github.com/cazala/synaptic/issues/70
https://github.com/cazala/synaptic/issues/12

Start by reading the discussion in Synaptic issues 70 and 12 and the BrainJS repository linked in the issue. Determine whether arrayfire-js should provide a backend for either neural-network framework, then define the integration scope and acceptance criteria before looking for implementation entry points; the issue names no files or tests.

索引モデルが issue の本文から書いたものです。