evaluation is done on client (Evaluator) side

Introducing new structure: instead of Evaluator/Client, now we
have Evaluator/Controller/PIDTable.
* Controller is a module keeping the state of the running program,
  that interfaces with a Supervisor TBD.
* Evaluator gets quoted Elixir programs and runs them, updating the
  state kept on a Controller.
* PIDTables initialize Controllers for Evaluators, and are yet TBD.

The code on this commit is not test as of now.