Better Error Messages

[CheaterCodes]

In my opinion, the biggest pain point in developing for chasm-lang right now are the bad and not very helpful error messages produced. Since #42, most expressions hold a reference to a ParseTree (though it might be null occasionally). This can be used to print the location in the source file as well as the actual expression text. However, this is currently not used in any exceptions.

A simple improvement would be to print additional information in the thrown exceptions. Alternatively, the system could even support printing multiple errors instead of simply failing at the first.

If you're interested in helping with this issue, please discuss here before opening a PR.