update-indices: now actually useful
publish-site: ignore SCSS
Refactor find_recent_pages

Now we have one cached function which finds all blog posts and 
another which returns n most recent posts
update-indices: fix logic for updating existing files

Since placeholder was removed, this only worked the first time it
generated a new index file
update-template: first version of a page content updater

This takes an existing HTML page, loads the existing data and 
populates the specified template
Big refactor

* Refactored to have a simple Page class representing an HTML page
  which holds (and caches) various accessor properties
* Added basic site config system
* Refactored HTML tidying into a function allowing it to be used
  pervasively
* Simplified update-template using Page & added support for post
  navigation links (which required Page & site config)