Add VgaFont device

[vinc]

A new device in /dev/vga/font will allow setting the VGA font from userspace. After that we can deprecate the whole vga command and remove it in the next version of MOROS.

[vinc]

There's an issue when doing read /ini/fonts/zap-light-8x16.psf => /dev/vga/font because read try to convert the file to unicode before printing it to the screen:

And copy doesn't work for device files.

[vinc]

This change will allow writing to devices.

We could also replace copy with a lisp script doing the following at its core:

(write-binary (second args) (read-binary (first args)))

[vinc]

This change allow reading binary files, so we can now do:

> read /ini/fonts/zap-light-8x16.psf => /dev/vga/font

In addition to:

> copy /ini/fonts/zap-light-8x16.psf /dev/vga/font

I'm not sure that the latter is the right thing because we could also expect the source to replace the destination instead of writing to it when it's a device file.