Use a dynamic array instead of a static array which we would simply
crash on overflow.  Always make it a power-of-two sized so we don't
end up doing a realloc() and a full array copy on every extend.

In the simple menu system, if we're showing a scrollbar at all, always
show at least one unit of it.

Support putting virtual kernels in high memory instead of using a
dedicated segment for it.  This both reduces the low memory footprint
by 64K, and allows for functionally unlimited labels (tested with over
a hundred thousand.)

Make "Hello, World!" a little bit more plain, but do print out its
arguments, if any.  Useful for testing.

Don't close the A20 gate (restore to previous state); leave it open.
This is good for performance, but also avoids a nasty race condition
when leaving protected mode to then quickly re-enter protected mode.

Clean up the interface to simple_pm_call so we generally can avoid a
bunch of push/call/pop/ret boilerplate.

Refactor the bcopy routine to be able to reuse the pm entry and exit
portion to call other "simple" protected-mode routines ("simple" in
the sense that no interrupt thunking support is present or expected.)

Note: consider whether or not it would be preferrable to move the
thunking support into low memory and have it be always present.

Suppress a warning about unused arguments.

We do dword accesses to the row buffer, so align it to 4 bytes.

Add macros __aligned() (which takes a byte count), and __alignas()
(which takes a type or expression whose type is used, same as sizeof).