Should change the output format to both a string and the stdio for an online execution (https://unitxsimulator.herokuapp.com/).

[supertask]

Expected behavior

The output format of UnitX is the stdio and a string.

Actual behavior

The output format of UnitX is only the stdio.

Steps to reproduce

Prints of the stderr in "eval_error_listener.py" and the stdin in "eval_visitor.py" should change. Also it should be looked for Util.dump(), and should be care at an object which UnitX provides. you may need to convert from an object into an string.