Attempt at better list markup.

Doesn't work for: templates in lists or explicit list block elements
(because it detects when it's in a list based on the parser), but it is
usually at least as good as the older version.

This kind of thing would be much easier if I represented the lists in
data rather than translating them as they are parsed. Not sure if I'll
do that soon though.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85247 b8fc166d-592f-0410-95f2-cb63ce0dd405