Move the prototypes for syslinux_shuffle_boot_[pr]m() from
<syslinux/movebits.h> to <syslinux/boot[pr]m.h>, which anyway has the
required structure definitions.  #include <syslinux/movebits.h> in
those files instead of relying on forward structure definitions.

- Add an API function to shuffle and boot which sets *all* RM registers;
- Move those structures to <syslinux/bootpm.h> and <syslinux/bootrm.h>

The shuffle and boot interface, including the library support, should now
work as advertised.  Add an ELF-loading module as a demo, and it's probably
useful for someone, too.

Initial checkin of a wrapper infrastructure for the "shuffle and boot"
interface, both real and protected mode.  This code automatically will
figure out the necessary sequence of moves, taking into account swaps
and overlaps as necessary.