ENH: getKeys timeStamped arg can now be a float

If a user wants the times returned by getkeys() to be relative to an
other time,  timeStamped  can be passed with a float or int as the
object type. In this case, the timeStamped  value is simply subtracted
from key times.

This allows for functionality like when using a clock and reseting it
when the flip occurs. However I find this simpler, and with less
overhead than using Clocks in many cases. It is also more accurate, as
the time right after the flip blocking code returns is used, so the flip
time is immune to the time it takes to run and code in win.flip()
following the actual flip time.
Depending on the time it takes to run any functions have been set to run
after the flip, this time difference could be biog enough to care about.

Ex:

flip_time=win.flip()
# do stuff
# ...
# get keys relative to the flip time
keyevents=event.getKeys(timeStamped=flip_time)
BF: getKeys isinstance was eval True to be an int

So if timeStamped=True in getKeys, events were being returned with the
time-1. Oops.

Now fixed for elif True: is checked before isinstance for float, int,
ENH: Added USB Keyboard mode support to ioSync

There is now a python method in the iosync interface that allows your
program to have the iosync hardware generate a keyboard press and
release event which are sent to the computer via the USB cable.

The duration of the keypress can be set as a param in the command
method.

The keypress event occurs in realtime with < 1 msec of uncertainty about
the time that the HID keyboard event packet was sent to the OS via USB.

To use this new feature, the ioSync.ino teensy 3 program must be
compiled with Serial set to Serial + Keyboard.

When the ioSync is connected to the computer, it will appear as a
generic USB keyboard to the OS ( it should be listed in the keyboard
section of your device manager).

The idea is that this should be able to be used to look at the software
only differences between OSs and libraries being used, as the key event
time is know precisely and in the same time base  used for key events
received by psychopy or iohub.
Merge pull request #566 from isolver/master

ENH: getKeys timeStamped arg can now be a float