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
Unsure how to handle this. I can duplicate the functionality in constructor of `Pages`, but that seems silly. I feel like I need to move the complexity up a bit higher, but then it means changing the array of files names, which I'm a bit iffy on as well.