Group pages within their own directory

Add `pages` as it's own content type, and move all page content into
the appropriate directory.

Any references to `layout` in the YAML front matter has also been
removed as it's implied by the content type. Except for `about.md`
which does explicity use a different layout.

source/_pages/dev.md

@@ -0,0 +1,22 @@
+---
+title: Developing this Website (WIP)
+---
+This site is built with [Sculpin][], a static site generator written in PHP, that generates a static HTML website from Markdown files and Twig templates. You can see the [source code on GitHub].
+
+## Extending Sculpin 
+
+- Custom Twig extensions
+- https://github.com/opdavies/sculpin-twig-markdown-bundle
+- https://github.com/opdavies/sculpin-gist-embed-bundle
+- https://github.com/opdavies/sculpin-content-generator-bundle
+
+## Front End
+
+On the front-end, I have used [PostCSS][] rather than Sass or Less, and [Tailwind CSS] for all of the styling, and some [Vue.js][] for the navbar and toggling the navigation menu on mobile. These are compiled with [Webpack Encore][] - a wrapper around Webpack, provided by Symfony.
+
+[PostCSS]: https://postcss.org
+[Sculpin]: https://sculpin.io
+[source code on GitHub]: https://github.com/opdavies/oliverdavies.uk
+[Tailwind CSS]: https://tailwindcss.com
+[Vue.js]: https://vuejs.org
+[Webpack Encore]: https://github.com/symfony/webpack-encore