Re: speed up unicode decomposition and recomposition

Thanks for the updated version, that was fast.  I have found a couple
of places that needed to be adjusted, like the comment at the top of
generate-unicode_norm_table.pl or some comments, an incorrect include
in the new headers and the indentation was not right in perl (we use
perltidy v20170521, see the README in src/tools/pgindent).

Except that, this looks good to me.  Attached is the updated version
with all my tweaks, that I would like to commit.  If there are any
comments, please feel free of course.