SWDAdapterBase: Implement clean base class for SWD hardware adapter support.
SWDProtocol: SWD protocol definitions.
SWDErrors: Add SWDNotPresentError.
mchck_swd: SWDAdapter implementation for mchck SWD firmware.

This firmware supports mchck, MSP430 Launchpad and Arduino.
adapter_factory: Helper to load adapter modules dynamically.
swd-identify: Beginnings of CPU identification/information utility.