Try to HLT the processor during idle.  All the events we care about
should have interrupts associated with them, except possibly the
serial console.  Try to deal with the serial console by waiting some
time before going into HLT, and giving the user the option of enabling
the serial console interrupt, on the assumption that the BIOS will
simply IRET.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

Add a new "UI" directive to specify a user interface module, instead
of abusing the DEFAULT directive.  This allows the DEFAULT directive
to be used for setting the default, even when the menu system is
enabled.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

When the Tab key is pressed, display a list of matching labels.  This
can be disabled via the NOCOMPLETE configuration command.  This is a
slightly modified patch by Sebastian Herbszt.

Allow the initrd to be specified on a separate line from command-line
options (append).  This apparently can help certain tools.

Move source files out of the root directory; the root is a mess and
has become virtually unmaintainable.  The Syslinux core now lives in
core/; the Linux and generic utilities has moved into utils/, and
copybs.com has moved into dos/; it had to go somewhere, and it seemed
as good a place as any.