Implement an advanced unit testing framework.

[reedriley]

We'll want to cover, at a minimum:

• Input
  1. Command line arguments.
  2. Source code to compile.
• Output
  1. Compiler output to stderr and stdout. (This will later require post-processing, of course.)
  2. Assertions on the generated code. (This isn't high-priority, and will require post-processing.)
  3. Expected output from the generated binary.