loose_break_needed(
list_stack,container_depth) ->needed
Decide whether a loose list needs a blank line before its next block
Records the block against the innermost open list and reports whether a blank line has to precede it. Loose spacing is emitted before a block rather than after one, so the last block of a list never picks up a trailing blank of its own and the first block of a list never gets a leading one.
Only blocks that are direct children of a list item count. container_depth
is the caller's current div plus blockquote nesting, compared against the
nesting the list was opened at, so a paragraph inside a blockquote inside a
list item is left alone.