New content model

*Not ready yet, WIP*

* [ ] Copy content from pages & posts over to destination directory intact
* [ ] Process markdown content matching glob to HTML
* [ ] Remove processed markdown content
* [ ] Attempt to allow for backward compatibility
* [ ] Refactor, this will be a mess
Actually, I think I lied about `htmlDir`. Links are crafted with the `htmlDir` in the path. Will need to figure this part out.