evkeyboardcontrol reads a keyboard directly from /dev/input

Much simpler version of https://github.com/openstenoproject/plover/pull/60

This allows you to use two keyboards: one for
normal input, and one exclusively for Plover.

Usage:

% sudo cat /dev/input/by-id/usb-Corsair_Corsair_K65_Gaming_Keyboard-if02-event-kbd | plover

Or, from a development environment:

% sudo cat /dev/input/by-id/usb-Corsair_Corsair_K65_Gaming_Keyboard-if02-event-kbd | PYTHONPATH=build/lib.linux-x86_64-2.7/ build/scripts-2.7/plover

Note that this just runs "cat" as root, not Plover. You might want
to fiddle with permissions a different way, that's your prerogative.

You probably want to disable the keyboard too,
this commit makes no effort to do that:

% dpkg -S =xinput
xinput: /usr/bin/xinput
% xinput
⎡ Virtual core pointer                          id=2    [master pointer  (3)]
..
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
..
    ↳ Corsair Corsair K65 Gaming Keyboard       id=18   [slave  keyboard (3)]
    ↳ Corsair Corsair K65 Gaming Keyboard       id=16   [slave  keyboard (3)]

% xinput disable 16

You can re-enable the keyboard with:
% xinput enable 16

Nobody knows what's going on with this /dev/input/by-id stuff, three
keyboards?  I guessed randomly.  Also, the webcam and is a mouse /and/
keyboard, just in case you were wondering.  Keep trying until it works:

% ls /dev/input/by-id
usb-046d_HD_Webcam_C615_76EEA130-event-if02
usb-Corsair_Corsair_K65_Gaming_Keyboard-event-if01
usb-Corsair_Corsair_K65_Gaming_Keyboard-event-kbd
usb-Corsair_Corsair_K65_Gaming_Keyboard-if02-event-kbd <-- the one that works for me
usb-Logitech_G700_Laser_Mouse_289B5DC10037-event-mouse
...