some multiboot2 comments

[Hollis Blanchard]

http://grub.enbug.org/MultibootDraft

I'm looking at implementing this now.

Module:
Because of the 'length' field in the tag header, the 'reserved' field
isn't actually needed. The 'length' field makes every one of these tag
structures inherently variably sized. Any data added later to this tag
will be skipped over by the reader.

Memory Map:
I'm not sure if we need this. The OS can get this information from
firmware (e.g. BIOS e820 map or Open Firmware) as easily as we can,
right? In general, I don't think we should convert firmware information
into the multiboot structure.

-Hollis