Compatibility normalization

[Piotr Karocki]

>if one must map some text with diacritics onto text in ISO Basic Latin
>letters (ASCII letters)
> for purposes beyond just fuzzy matching, it is usually better to use (with
> awareness of the
> language in use) an appropriate transcription scheme rather than just
> removing all diacritics;
> see German DIN 91379 for European languages[3], Vietnamese Telex[4],
> Gwoyeu Romatzyh for
> Mandarin tones[5], Revised Romanisation for Korean vowels[6], etc.)
Such mapping is useful to create filenames compatible with POSIX portable
filename characterset. And such charset is meant to create filenames that
can be used in any existing file system.