Enabling header links via with_toc_data and bbalter solution

which is almost OK, but I'm not happy about the crappy anchor names redcarpet assigns.  Overriding this with a custom TOC handler *would* be possible if this didn't have to be `jekyll --safe` compatible, but that's kinda the deal with github pages.  One option would be to drop the `safe` option, add a li'l plugin to make sluggy anchor ids a la `#singular-resources` and require all compiled resources to be committed :scream_cat:.  Opinions wanted!