Added support for comments.

Problem: The parser was not handling comments.

I updated the parser to ignore comments.
Made apply work for any Function, not just BuiltinFunctions.

There's no reason why apply can't work on any Function.
Merge pull request #18 from JonathanAquino/apply

Made apply work for any Function, not just BuiltinFunctions.
Merge pull request #17 from JonathanAquino/comments

Added support for comments.
Improve stack traces.

This change adds to the stack trace the form that we attempted to evaluate.
While this makes the stack trace more verbose, it does make debugging a lot
easier.
Merge pull request #19 from JonathanAquino/better-stack-traces

Improve stack traces.