ENH: Latest ioSync Teensy3 software

- uses faster digital read and digital write functions.
- Adds EXT_LED define for use in controlling an external LED (intended
to be the status LED on the ioSync enclose project)
- Adds Analog output pin define. (python API usage no yet done)
- Adds code related to software based teensy3 reset, restart, and last
reset reason reporting. Python API integration TBC.