Directory Walker section

An directory walker source section yields a hierarchy of items with paths from a filesystem using `os.walk()`_.

>>> infologger = """
... [transmogrifier]
... pipeline =
...     source
...     logger
...
... [source]
... blueprint = collective.transmogrifier.sections.dirwalker
... dirname = collective.transmogrifier:.
... sort-key = python:not basename.lower().startswith('dir'), basename
...
... [logger]
... blueprint = collective.transmogrifier.sections.logger
... name = logger
... level = INFO
... """
>>> registerConfig('collective.transmogrifier.sections.tests.dirwalker',
...                infologger)
>>> transmogrifier('collective.transmogrifier.sections.tests.dirwalker')
>>> print(handler)
logger INFO
  {'_path': '/', '_type': 'Folder'...
logger INFO
  {'_path': '__init__.py'...
logger INFO
  {'_path': 'sections/', '_type': 'Folder'...
logger INFO
  {'_path': 'tests/', '_type': 'Folder'...
logger INFO
  {'_path': 'sections/dirwalker.py'...
logger INFO
  {'_path': 'sections/breakpoint.py'...