Develop a hardened SerialParser implementation suitable for reading/writing XBEE API mode requests

[davidkirwan]

The Ardtweeno system will be far more useful if it is capable of communicating with XBEE radios running in API mode.

[davidkirwan]

Considering the removal of the API key handling out of the node firmware, and put it in the parser potentially. Match the API keys with the Mesh network node id's before posting packets to the gateway. This separation of concerns will allow each node to focus on the transmitting or retrieval of data rather than any unnecessary administration.