Feature/templating engine

This branch drops in [a premade php library](https://github.com/1337/pop) to serve dynamic pages. 

To render a page with the default template, include `pop.php` at the beginning of the file:
```
<?php require_once('pop/pop.php'); ?>

(more content)
```

It also contains a filesystem database, but we will only be using its templating engine for now.