Should be enough to (1) talk to the Java API and (2) provide
a JSON API for the world.

This is really just experimental. MMT should be integrated directly
w/o JSON if possible to avoid nonsensical serialization.

- code goes into /src

- prose in /doc

- /experimental is a playground

- I'm going to use graphcli to explore the GraphDB Java interface
  as the tutorials use Java.

- I'll look into Scala later (ideally tomorrow).