Implement wctype.h

Implement the wctype following http://pubs.opengroup.org/onlinepubs/7908799/xsh/wctype.h.html

• Types
  • wctype_t
• Functions
  • iswalnum
  • iswalpha
  • iswcntrl
  • iswdigit
  • iswgraph
  • iswlower
  • iswprint
  • iswpunct
  • iswspace
  • iswupper
  • iswxdigit
  • iswctype
  • towctrans (stub missing)
  • towlower
  • towupper
  • wctrans (stub missing)
  • wctype

See https://git.musl-libc.org/cgit/musl/tree/src/ctype for a good reference implementation.