Improve styling of command examples.

These example commands are kind of like quotations so wrap the
paragraphs in blockquote tags.  This gives better results in most
browsers when styles are not used.

Then improve the styling overall to be more responsive: the results
are bad when linebreaks are placed in the middle of program options
or filenames, so try to prevent that by only allowing line breaks
where there are spaces.

Then, indent all but the first line to try and visually convey that
this is a continuation of the previous line.