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!