IntanThread now handles TTL inputs and generates its own timestamps.

The IntanThread can report TTL events on its 6 input channels. This was tested
with an Arduino; input detection is fast and reliable.

The IntanThread also generates its own timestamps, allowing the software to move
toward a framework in which timestamps come from input sources, rather than
from the RecordNode.

Finally, an ArduinoOutput module was added, which allows the software to
communicate with an Arduino via serial output.