iohub 2.0 related changes to date

!!! These changes are NOT backwards compatible !!!

1) Removed KeyboardChar Event type. Full implemented on Windows. OS X and Linux must be updated to also no longer generate KeyboardChar events. 
2) Added duration field to KeyboardPress event type
3) Started work on psychopy side wrappers for iohub devices. Currently only keyboard device is implemented (feedback requested please if possible) on Windows OS. 
     * See psychopy.iohub.client.keyboard.py for new keyboard device interface.
     * Until 1) is done, Linux and OSX will not work. Will do this as a priority.