Inject OpenGraph information into all pages

Every page should have the following basic information:

```

```

The above should be created automatically by injecting the following onto each page:
```
---
title: "foo"
image: "https://fff.png"
url: "https://foo"
---
```

where the title and URL are specific to the page and the image is specific to the document.

> Note: PDF and CHM do not support front-matter!