Merge branch 'wide-strings' into 'master'

src/header/mod.rs

src/header/wchar/mod.rs

src/header/wctype/casecmp.rs

src/header/wctype/cbindgen.toml

src/header/wctype/mod.rs

tests/Makefile

tests/expected/wchar/wcscasecmp.stderr

tests/expected/wchar/wcscasecmp.stdout

tests/expected/wchar/wcsncasecmp.stderr

tests/expected/wchar/wcsncasecmp.stdout

tests/expected/wctype/towlower.stderr

tests/expected/wctype/towlower.stdout

tests/expected/wctype/towupper.stderr

tests/expected/wctype/towupper.stdout

tests/wchar/wcscasecmp.c

tests/wchar/wcsncasecmp.c

tests/wctype/towlower.c

tests/wctype/towupper.c