As part of investigation for #483, I found that when minifying the
content for the site, Hugo was removing the lovely whitespace that was
needed by the `pre-line`s inside `.p-content` blocks.

As a workaround, we can wrap the `.p-content` in a `<pre>`, which will
then retain the whitespace. We'll then need to ensure that it's styled
as regular text, rather than the actual `<pre>` tags.

*However*, this does not quite work because then microformats-ruby does
not parse `.p-content` correctly. Instead, we need to have the
`.p-content` container as a `<div>` and then place it inside a `<pre>`
to format it correctly.

Note that we also need to make sure that the `.p-content`s are now
max-width'd, but only if it's on an actual post page, otherwise it would
show up as max-width'd on the h-feed, too.

Finally, we need to make sure that we use the `pre-line` so it correctly
word wraps, otherwise we'll see horrible scroll bars and it'll be a
pretty naff experie...