Sugguestion: separate input and output driver

[Bean]

Currently, input and output are bundled together, this make it quite
difficult to extend.

Input:
Keyboard, Serial

Output:
Text mode, Video mode

Now, the binding is fixed using individual module:

Keyboard + Text = console
Keyboard + Video = gfxterm
Serial + Text = serial
Serial + Video = ?

And there are mixing as well.

If we separate them, it would make things much clear. For example, the
grub_term structure can be split into two mutually exclusive parts:

struct grub_term =
{
  .name,
  .init,
  .fini,
  .putchar,
  .getcharwidth,
  .checkkey,
  .getkey,
  .getwh,
  .getxy,
  .gotoxy,
  .cls,
  .setcolorstate,
  .setcursor,
  .flags,
  .next
};

=>

struct grub_input
{
  .name,
  .init,
  .fini,
  .checkkey,
  .getkey
  .flags,
  .next
}

+

struct grub_output
{
  .name,
  .init,
  .fini,
  .putchar,
  .getcharwidth,
  .getxy,
  .gotoxy,
  .cls,
  .setcolorstate,
  .setcursor,
  .flags,
  .next
}

Integration between input and output:

Input driver <=> console driver <=> Output driver

The console driver is the central part. It accepts virtual key from
the input driver, and write to the virtual screen provided by output
driver.

-- 
Bean