Factored index making out of compile-website.

New proc: 'add-article-collection'.
Refactored main. Moved commands to namespace 'tclssg'
scriptConfig moved to ::tclssg. Use as library.

Replacing scriptConfig with ::tclssg::script finally gets rid of
all those upvars. Tclssg can now be sourced from other scripts
and used as a library.