Kick out Multiboot 2 draft as a branch. Initially it is
identical to Multiboot 1, except for the magic numbers.
* doc/multiboot.h: Rename to ...
* doc/multiboot2.h: ... this. Update all users.
(MULTIBOOT_HEADER_MAGIC): Replace with ...
(MULTIBOOT2_HEADER_MAGIC): ... this. Update all users.
(MULTIBOOT_BOOTLOADER_MAGIC): Replace with ...
(MULTIBOOT2_BOOTLOADER_MAGIC): ... this. Update all users.
Use more standard `doc' directory.
* docs: Rename to ...
* doc: ... this. Update all users.
* doc/multiboot.texi: Fix an obsolete reference to `docs' directory
in GRUB distribution.