- Moved linked list support to new "list.c" file.

- Moved linked list support to new "list.c" file.
  Structure definitions are still in project.h,
  function prototypes are now in "list.h".
- Added support for "struct list_share", which is identical
  to "struct list" except it saves memory by not duplicating
  the strings.  Obviously, this only works if there is some
  other way of managing the memory used by the strings.
  (These list_share lists are used for lists which last
  for only 1 request, and where all the list entries are
  just coming directly from entries in the actionsfile.)
  Note that you still need to destroy list_share lists
  properly to free the nodes - it's only the strings
  which are shared.