ioSync enhancements

The ioSync software (teensy 3 program and the computer side python
interface) and base teensy 3 / 3.1 pin out functionality has now been
verified for:
- 8 digital inputs,  currently at 1000 Hz on MCU
- 8 analog inputs, currently at 1000 Hz on MCU, 0 - 3.3 V input range,
12 - 13 usable bits of resolution.
- 8 digital outputs.

- MCU usec clock to psychopy / iohub time base syncronization has been
verified to be within +/- 0.5 msec. Can likely get it better with more
effort.

ioHub interface is working well it seems.

Examples are provided using psychopy.iohub for using each pin type and
testing time syncing.

As usual, doc's are very light at the moment. ;)
Merge pull request #534 from isolver/master

ioSync enhancements