first steps in making odml part nested, some functions switched off...
TreeIterator can be limited to a certain search depth.
some backflip: Sections and SectionIterators have File pointer again.
File.hasSection and getSection working again.
new method: Section::hasSection takes depth argument to limit search
depth.
File::hasSection relays to Section::hasSection
rename File::getSection > findSection. Takes depth argument to limit
the search depth.
implementation findSection method in Section.
TreeIterator sets negative depths to unlimited... is that good?
test of findSection and hasSection, TestSection needs some more work