A directory type module handle accesses to directories. This is
usually done by creating a directory listing of the contents in the
directory, or finding a suitable index file to be returned instead.
There can only be one directory module in a virtual server.
The module type constant for directory modules are
MODULE_DIRECTORIES.
mapping parse_directory( RequestID id )
Returns a normal response containing either a suitable directory
listing or an index file. The path to the directory being listed is
found in id->>not_query.
