Caps lock now works as caps lock, not as shift lock.
This new design will allow implementing a working tty, such that stdin is
the only way to access the keyboard, instead of the current hacky way of
using a special system call to read from the keyboard.
Added a new system header file <sys/keycodes.h> defining the constants for
every key on the keyboard. This will be used in future APIs.
The main change is to split the keyboard driver into a class that reads
from the keyboard, while another class handles the translation into
printable characters (if possible). This allows a terminal driver based
on logical key presses and printable characters, instead of a terminal
driver based only on unicode-ish codes.
