Moving unittest code into tests directory.

debug.py and debugcommunity.py have been split into one file per class
and moved into tests/debugcommunity/.  Import statements have been
modified to reflect this change.

Other minor changes:
- DebugNode now takes community as a parameter instead of calling
  set_community
- Method names in DebugNode have been modified from create_..._message
  into create_...
- Documentation has been added.