Scala API/DSL alignment

[fs...@posteo.de]

Hi all,

I started writing a short doc that summarized our current approaches to 
interacting with SystemML in Scala:
https://docs.google.com/document/d/1ntdfmSBB83zdcWZl2iv4yMsrA3ZHDM-mzX5lMfFpfeo/edit?usp=sharing

The doc contains currently implemented features as well as 
considerations for future development. This should make the development 
of new Scala features a little bit more aligned by basing it on the same 
types and agreeing on supported approaches. At the same time it can 
serve as a starting point for documentation concerning Scala users.

It is by no means complete and I encourage everyone (especially Scala 
users!) to comment on it or add/remove things.


-Felix