hub.darcs.net :: falsifian -> sexprj -> changes

Also expose the list of atom characters and whitespace characters, and document constraints on atoms that should be respected.

I chose the versions I currently have installed on my system. Probably a wide range of other versions will work; this can be changed later.

Also set default-language since that's needed for newer cabal-version. I choses Haskell98 because I think that's what I had in mind when I was writing this.

This is the diff between the latest version of this repository I had and the first commit (c082390a) in a copy of the project I'd put on GitLab at https://gitlab.com/falsifian/sexprj

This is git commit dbbc2353 (the latest) from a version of the project I exported to git at https://gitlab.com/falsifian/sexprj/ . I plan to move development back to darcs.