stylize section names

Apply the same cyan-bold styling to the section-names in the section
headers as they get in the usage.  Hopefully this will help create a
visual cue that they are the same thing.

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
kngclick: uglier, more effective section styling

This rewires the section styling by overriding write_heading and
heuristically guessing if the heading corresponds to the section.

If so, we do the styling (including, this time, a bold colon) there.
Also, add a kludge to de-pluralize "Commands" in the section header, for
clarity and consistency with the usage.

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>