Add more testing for the CSE machine and the Conductor evaluator

[AaravMalani]

The parser, resolver and validator are pretty well tested. However, the CSE machine is basically untested so far. There are two aspects of testing needed to be done

1. Testing the CSE machine: This is something Python chapter 2 (+ 3?) support #81 introduces extensively for Python 1 and 2. It builds a testing framework which uses runInContext to evaluate programs. It still lacks support for Python 3 and 4, although that

2. Testing Conductor-specific features: The issue with the runInContext method is it bypasses the Conductor entirely. Features like IO streams from Use Conductor-based streams for StdIO #107 and Autocomplete from Add Autocomplete and Syntax Highlighting #109 require a Conductor instance. IMO, there probably needs to be a mock Conductor framework which is testable