Pacman easter egg

[marimeireles]

Theoretically adding this piece of code:

                    if (case_insentive_equals(xvega_input[0], "PACMAN"))
                    {
                        nl::json pacman;
                        std::ifstream i("../examples/pacman.json");
                        i >> pacman;
                        publish_execution_result(execution_counter,
                                                 std::move(chart),
                                                 pacman);
                    }

And the json of the pacman: https://vega.github.io/vega/examples/pacman.vg.json
Should allow us to play pacman on the jupnotebook, however we get a bad_allocation_err with no other info.

This issue tracks my progress on debugging this.