Document and run current CFDP implementation

[aywaldron]

Need to document usage for users and understand codebase and how to use it.

[aywaldron]

In order to get the example sender and receiver scripts at /ait/dsn/bin/ait_cfdp_start_receiver.py and /ait/dsn/bin/ait_cfdp_start_sender.py to work, I had to do the following:

• Add config/mib directory to the ait-core installation
• Create file to send in /ait-core/ait/dsn/cfdp/datasink/outgoing/medium.txt

The code automatically created a ait/dsn/cfdp/datasink directory in the ait-core installation containing incoming, outgoing, pdusink, and tempfiles subdirs.