Makefile: change boot.bin to image.bin
boot.s: remove VIDSEG
boot.s: rewrite the MBR magic number code
boot.s: use DS register
Makefile: disable linker address translation
boot.s: Remove address translation

Now that _start is placed at 0x0, we don't need to calculate $msg1
relative address.
boot.s: Small format fixes
boot.s: Add code for rebooting on keypress.