implemented basic multi-process debugging

* anonymous functions and receive use the -> (match) operator.
* spawn initializes another Evaluator server.
* PIDs are being passed around as binaries, which kinda work for
  now, but can cause problems on the future.
* coded the <- operator explictly, to deal with PIDs as binaries.
* `self` still have to be specified, as for now it is getting the
  PID of the Evaluator process, not the debugged one.