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
Remove old forward declaration.
Improve some id_manager comments.
Clean header id generation.
Clean final id generation.
Extract 'order' from `id_placeholder`.
Extract `id_data` from `id_placeholder`.
Combine 'child' and 'unresolved' id states.
Pull the resolved state from `id_placeholder`.
Stop storing generated ids in `id_placeholder`.

Placeholders are now completely constant.
Improve the handling of file ids.

Instead of messing around with the section's id, leave it alone and
check for a file id whenever looking up the current id.
Mark up const use of `id_state` and `id_placeholder`.
Make entity data const where possible.
Split up the id manager file.
Remove old forward declaration.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85258 b8fc166d-592f-0410-95f2-cb63ce0dd405
Improve some id_manager comments.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85259 b8fc166d-592f-0410-95f2-cb63ce0dd405
Clean header id generation.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85260 b8fc166d-592f-0410-95f2-cb63ce0dd405
Clean final id generation.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85261 b8fc166d-592f-0410-95f2-cb63ce0dd405
Extract 'order' from `id_placeholder`.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85262 b8fc166d-592f-0410-95f2-cb63ce0dd405
Extract `id_data` from `id_placeholder`.

git-svn-id: https://svn.boost.org/svn/boost/trunk/tools/quickbook@85263 b8fc166d-592f-0410-95f2-cb63ce0dd405