Possibility of parse errors in the ADK USB receive call

[psigen]

https://github.com/platypusllc/firmware/blob/master/firmware/firmware.ino#L283

Currently, we assume that adk.read() will always receive the entire contents of a single command. This is not guaranteed, it could receive half of a packet, and append the other half to the beginning of the next read operation.

If this fragmentation continues, it can corrupt a chain of packets indefinitely if they happen to alias against the USB receive buffer size.

We should treat USB input like any other serial input:

• read into the buffer
• manually checking for EOL characters
• process any completed substring
• memmove() the unused remaining buffer