Get the checksum working correctly.

I will never express my hapiness in this log message.
Basic CLI module.
Got the POSIX and SDL data layer defines mixed up.
Descriptions for CLI commands.
Two display utilities needed for cli and displaying stuff, yeah.
Some safeties for the display utilities.
Try to add arguments to the cli.
Add in a ping command for the cli.
Move toward a radio-agnostic stack.

The unit tests can now be run using either posix sockets or the sdl
for an interface downward.