For the most part, all the keywords for a standard mtree spec now have a
function to produce the contents for a creator.
These are used in the "walk" function, and will be used next in the
"check" logic.
This is still a WIP, as the DirectoryHierarchy produced from the current
Walk() is not all-together a valid document.
Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>
