ENH: Allow directory of files to be indexed
ENH: Allow directory of files to be indexed

In the Data directory, there may be sub-directories of files that need to
be kept separate, but all of them need to be indexed.

thewtex/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,thewtex/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,thewtex/SimpleITK-Notebooks