FAT has a somewhat obnoxious rule: byte E5 in the first position is
encoded as 05.  If it was *always* that case we could simply fold it
into the codepage tables, but that rule applies only to the first
character.

Note that in the common codepages (incl. 437), E5 is lower-case sigma
(σ), which we currently upper case to upper case sigma (Σ, E4)
preventing a match -- which DOS *doesn't* do (it thinks of the Greek
characters as symbols, not subject to case distinctions.)  Putting
that special case in the codepage-generation scripts seems too ugly,
though.

Add additional codepage data from the Unicode Consortium.
Additionally, add support for generating codepage files for the case
where the filesystem codepage and the display codepage do not match.
The standard Makefile doesn't actually do that, however.

"Bytes left" should be "bytes read"

We don't need the ANSI engine in mboot.c32.

Default to \n -> \r\n conversion in the ANSI and xserial modules,
rather than relying on escape codes to make that behave.  This
effectively means that as far as the serial port is concerned, this
behavior cannot be turned off (with less than having the xserial state
machine interpret this sequence) and the escape code *should not* be
used.

That is fine for our applications, though.

Avoid crashing in the presence of unnamed submenus.