organize toc repos

[jonschlinkert]

I've learned that you may need to generate a toc and then inject it at a different point in the build. This repo does this correctly. We have a few TOC repos, the code here and in those repos will be reorganized:

• markdown-toc: actually creates the toc/json. this repo is ok for now
• template-toc: attempts to create a toc from a markdown document, then inject it. it's not done correctly though. we might deprecate this one