Create Directory Object about schemas

[ikiril01]

We've had some additional requests for this Object, so I'm notionally adding it as a milestone for CybOX v2.1.

[gtback]

We want to keep this relatively simple for now, and not deal with the complexity of different file systems, until we separate the file content vs. file system properties on File/WinFile/UnixFile. The simple represntation should be in 2.1, though.

[ikiril01]

Some possible properties for the v2.1 representation:
*is_compressed (Boolean; whether the directory is compressed or not)
*is_hidden (Boolean; whether the directory is hidden or not)
*is_offline (Boolean; whether the directory is offline or not)
*is_readonly (Boolean; whether the directory is readonly or not)
*is_symbolic_link (Boolean; whether the directory refers to a symbolic link or not)
*Directory_Path (String; the path to the directory, akin to the File_Path in the ObjectType)

[ikiril01]

This requires more investigation of the nuances, especially with regards to the relationship with the File Object, so we will leave it out for 3.0.

[ikiril01]

Context: this has been requested by several community members in the past, and would be useful for digital forensics related use cases, more accurately describing the operations of malware (i.e. in MAEC), and for specifying directory-related indicators (i.e. in STIX).

LOE: Medium