Proof of Concept: Embedded Scala DSL

[fschueler]

As discussed in the related Jira (SYSTEMML-451) I have started to 
implement a prototype/proof of concept for an embedded DSL in Scala.

I have summarized the current approach in a short document that you can 
find on github together with the code: 
https://github.com/fschueler/emma/blob/sysml-dsl/emma-sysml-dsl/README.md
Please note that current development happens in the Emma project but 
will move to an independent module in the SystemML project once the 
necessary additions to Emma are merged. By having the DSL in a separate 
module, we can include Scala and Emma dependencies only for the users 
that actually want to use the Scala DSL.

The current code serves as a proof of concept to discuss further 
development with the SystemML community. I especially welcome input from 
SystemML Scala users on the usability of the API design.
Next steps will include the translation from Scala code to DML with 
support of all features currently supported in DML, including control 
flow structures.
Also, a coherent way of executing the generated scripts from Scala and 
the interaction with outside data formats (such as Spark Dataframes) 
will be integrated.

I am happy to answer your questions and discuss the described approach 
here!

Felix