Add support for function/module docstrings

[darrencruse]

In addition to the "atoms" retaining line/col info for source maps, there is also source for passing comments in the source out to the generated code.

Unfortunately I had trouble getting that to work cleanly though and disabled it - right now source comments do not transfer to the generated javascript code.

It seems like function docstrings would be a wonderful compromise though. i.e. being able to describe what functions do and what the inputs and outputs are in a way that can be extracted seems the most important kind of comment and s-expressions make that much wonderfully easy (i.e. if these are a standard option for function declaration s-expression forms they're much easier to deal with than arbitrary comments anywhere/everywhere which is what I'd been trying to support).

https://en.wikipedia.org/wiki/Docstring