process class, D2Process, and the abstract class from which it derives,
DProcess. This class provides DHCP-DDNS specific event loop and business
logic.

The following new files have been added:

   src/bin/d2/d_process.h - defines the DProcess base class
   src/bin/d2/d2_process.h - defines the D2Process class
   src/bin/d2/d2_process.cc - implements the D2Process class
   src/bin/d2/tests/d2_process_unittests.cc - initial unit tests