Add smalltalk support

Smalltalk has two main git-friendly file mappings: the old "chunk format" liberally sprinkled with exclamation marks (stripped out by `ignore_chunk_descriptions` and `ignore_chunk_separators`) and "[filetree](https://github.com/dalehenrich/filetree)".

The latter has the unfortunate characteristic of not terminating files with a newline, hence the `-printf '\n'` argument to `find`.

This is not perfect - we throw away all class declaration data, which are stored in json files - but rather a lot better than nothing.

In keeping with the rest of `code-words`, we throw away comments ("quote encoded ""with nesting"" ").