Fix horizontal scrolling on mobile devices

`<pre>` and `<code>` blocks were causing Chrome Mobile for Android version 35 under Android
version 4.1.2 (Samsung Galaxy SIII Mini) to add horizontal scrollbars to pages where
they were present.

Fix this by:

- making `<code>` elements display as inline blocks:
a) `inline-block` elements will not break apart as was happening prior to b08b53b
b) because `<code>` elements are displayed (at least by Chrome) as `inline`, setting the `overflow`
property has no effect

- setting the `overflow` property for `<pre>` block objects, which adds a horizontal scrollbar
beneath the element