bring extras/arcfn-docs in sync with the arclanguage.github.io repo

I'm still uncertain how to organize things.
1. Ken's docs really belong inside each variant like arc3.1, anarki, etc.
2. Using a project-specific gh-pages branch would be out of sight during
development.
3. Keeping the pages in the repo might itself not be that visible, and would
introduce new deployment issues.

And then there's the question of how to keep help/ in sync with these docs..
update docs for swapped args of subst