This is a follow-on in that the old utf8 code was still being
used in ncgen to convert utf8->utf16 when converting cdl to Java
(see genj.c).

The new code apparently has no utf16 support, but it does have
utf32 support. Converting utf32 -> utf16 can be approximated by
truncating the 32bits to 16 bits, unless the top 16 bits are
not zero. This latter condition is unlikely to be common because
it implies use of some rather obscure characters.

So solution is to convert to utf32 and truncate to 16 bits to
get utf16. An error is reported if the high-order truncated 16
bits are not zero. If we get complaints, then I will figure out
how to convert full utf32 to a utf16 pair.

Also removed the old code from ncgen.

This is a follow-on in that the old utf8 code was still being
used in ncgen to convert utf8->utf16 when converting cdl to Java
(see genj.c).

The new code apparently has no utf16 support, but it does have
utf32 support. Converting utf32 -> utf16 can be approximated by
truncating the 32bits to 16 bits, unless the top 16 bits are
not zero. This latter condition is unlikely to be common because
it implies use of some rather obscure characters.

So solution is to convert to utf32 and truncate to 16 bits to
get utf16. An error is reported if the high-order truncated 16
bits are not zero. If we get complaints, then I will figure out
how to convert full utf32 to a utf16 pair.

Other changes:
1. removed the old code from ncgen.
2. changed UTF8PROC_DLLEXPORT (in utf8proc) to EXTERNL
   and added appropriate includes. This should fix
   issue #404,
   but since we cannot duplicate the failure, I am not quite
   sure.