Implemented basic Get Attributes All parsing
o Still very basic; each class/instance needs to be able to parse a set
  of commands Get/Set Attribute(s) All/Single; we parse them statically, not
  dynamically based on the specific class/instance.
o The unconnected_sent must accept a request composed only of a request_path, and
  it may have a pad byte if length is odd.
o Added some tests to enip_test.py unit-CIP.