Add golden tests that illustrate parsing results

[andrewthad]

This adds a simple integration test that serves two purposes:

1. Illustrate the ASTs resulting from parsing simple expressions. A combination of pretty-show and dropping all location annotations results in output that is at least somewhat readable. It would be better to manually write a pretty printer for the expression type, but that's more difficult to do.
2. Confirm that the parser works as expected.

Concerning goal (2), I have a concern. I'm trying to use a string template in the input file, but the parser does not seem to understand what I've done:

         [ Chain
             ()
             (Symbol () "print" :||
                (Paren () (Just (String () "The dog is `years` years old!" [])) :|
                   []))
         ]) :|

I expected that years would be broken apart from the other stuff, but I might just be using string templates incorrectly.

[Zankoku-Okuno]

Only double-quoted strings allow templating. The single-quote strings are there specifically so that the only escaping that needs to be done is for single-quotes.

[andrewthad]

Thanks, I had missed that. I've done a force push correcting the test.