added init for DirectoryStore
added `get_dbSize` method to DirectoryStore
added `fetch_data` method to DirectoryStore
added handling of createSubDir setting to DirectoryStore
added method to get file path to DirectoryStore
prohibit switching on DirectoryStore
allow DirectoryStore to inherit from BdbStore (for metadata)
added `store_data` method to DirectoryStore
added `delete_data` method to DirectoryStore
DirectoryStore inherits several methods from BdbStore

 * `store_metadata`
 * `fetch_metadata`
 * `clean`
 * `flush`
added `clear` method to DirectoryStore
moved DirectoryStore to end of module
made DirectoryStore iterable
fixed bugs in DirectoryStore methods
fixed some variable name bugs in DirectoryStore
tests: improved docstrings in testBaseStore
tests: added tests for DirectoryStore
added DirectoryDocumentStore
added DirectoryRecordStore
tests: added tests for DirectoryDocumentStore