* lib/mbchar.h: Include <uchar.h> instead of <wchar.h>, <wctype.h>.
(struct mbchar): Use char32_t instead of wchar_t.
(mb_casecmp, mb_caseequal): Use c32tolower instead of towlower.
(mb_isalnum): Use c32isalnum instead of iswalnum.
(mb_isalpha): Use c32isalpha instead of iswalpha.
(mb_isblank): Use c32isblank instead of iswblank.
(mb_iscntrl): Use c32iscntrl instead of iswcntrl.
(mb_isdigit): Use c32isdigit instead of iswdigit.
(mb_isgraph): Use c32isgraph instead of iswgraph.
(mb_islower): Use c32islower instead of iswlower.
(mb_isprint): Use c32isprint instead of iswprint.
(mb_ispunct): Use c32ispunct instead of iswpunct.
(mb_isspace): Use c32isspace instead of iswspace.
(mb_isupper): Use c32isupper instead of iswupper.
(mb_isxdigit): Use c32isxdigit instead of iswxdigit.
(mb_width_aux): Use c32width, c32iscntrl instead of wcwidth, iswcntrl.
* lib/mbiter.h: Include <uchar.h> instead of <wchar.h>.
(mbiter_multi_next): Use mbrtoc32 instead of mbrtowc.
* lib/mbuiter.h: Include <uchar.h> instead of <wchar.h>.
(mbuiter_multi_next): Use mbrtoc32 instead of mbrtowc.
* lib/mbfile.h (mbfile_multi_getc): Use mbrtoc32 instead of mbrtowc.
* lib/mbscasestr.c (knuth_morris_pratt_multibyte, mbscasestr): Use
c32tolower instead of towlower.
* lib/exclude.c (string_hasher_ci): Use char32_t, c32tolower instead of
wchar_t, towlower.
* modules/mbchar (Depends-on): Add uchar, c32isalnum, c32isalpha,
c32isblank, c32iscntrl, c32isdigit, c32isgraph, c32islower, c32isprint,
c32ispunct, c32isspace, c32isupper, c32isxdigit, c32tolower, c32width.
Remove wchar, wctype-h, iswblank, iswdigit, iswxdigit, wcwidth.
* modules/mbiter (Depends-on): Add mbrtoc32, uchar. Remove mbrtowc,
wchar.
* modules/mbuiter (Depends-on): Likewise.
* modules/mbscasestr (Depends-on): Add c32tolower.
* modules/exclude (Depends-on): Add c32tolower.
* doc/strings.texi (C strings): Fix typo.