Responsive fixes and minor aesthetic change.

* Images scale to fit the container.
* <pre> code scales to fit and scrolls.
* Inline <code> (not in a <pre>) doesn't justify: it looked shite.
* Background color is slightly lighter, less dank.
* Title and subtitle are now Arvo font.
* Title and content shrinks to fit smaller screens.
* Body decreases font-size for smaller screens.