[HarfBuzz] Standalone Unicode support library

[Grigori Goronzy]

Hi everyone,

I have put together a simple standalone Unicode support library that
provides just the functionality HarfBuzz needs. This should be useful
for the people that want to use HarfBuzz on non-Unix platforms. It's
much, much smaller than ICU or glib, less than 200 KB binary size on
x86_64, and is implemented in plain C89 with no extra dependencies.

The library is called UCDN (which stands for Unicode Database and
Normalization) and is available from Github:

https://github.com/grigorig/ucdn

Hangul Jamo (de)composition is not yet implemented, but apart from that
I haven't found any obvious differences to glib's Unicode functions.

The included HarfBuzz connector hb-ucdn.h makes it really easy to use
with HarfBuzz: just create a hb_unicode_funcs_t structure with
hb_ucdn_make_unicode_funcs and pass that to a hb_buffer_t with
hb_buffer_set_unicode_funcs.

Best regards
Grigori