ENH: Gazepoint GP3

GP3 tracker interface now supports:
- connecting / disconnecting from device
- start / stop recording sample data (binocular eye sample events)
- stream / save samples when recording. gaze x, y fields populated.
- getPosition() returns the GP3 latest provided FPOG X,Y

Note: - Calibration is not yet implemented.
- event times are set to time sample was received by iohub. Sample delay
calc. needs to be completed so sample times can be in iohub / psychopy
time base.
ENH: OS X ioHub keys

Based on my mac mini KB, The keyboard events are generating .key and
.char values as expected for all keys I have tried, with following
exceptions:

 - the  4 arrow key .char values.
- modifier constants in modifier list are not yet switched to standard
values (those matching psychopy).

Other than that, please run the iohub/keyboard.py demo and test out how
the keyboard mapping is working for your box, bk, local.

*** You need to add your IDE or the terminal.app to the list of
authorized app’s for accessibility api. Otherwise, you will get NO
keyboard events.

Thanks!
Merge branch 'master' of git://github.com/psychopy/psychopy
Merge pull request #679 from isolver/master

OSX iohub keyboard event rework is getting close.