The org mode toc OPTION does not just support true/false - it also allows
specifying the max headline level [1] to be included in the toc.
[1] headline level as seen in org mode - not the html tag level
this introduces the PropertyDrawer node to make it easier to access the
properties associated to a headline - normal drawers don't parse their content
into kv pairs
Until now we expected the .org file to print back to itself - we can't do that
when the input is not pretty printed already - with the introduction of blocks
with unindented content that will be the case.
