1.6.4: Windows and Misc. Updates

• Update Fips codes (Boris Zentner)
• Several issues with the MinGW build were fixed. (Thomas Pöchtrager. Github
  #46.)
• Use a constructor in pread.c to ensure the critical section is always
  initialized. (Thomas Pöchtrager. Github #47.)
• Added missing include of io.h on Windows. (Thomas Pöchtrager. Github #49.)
• Fixed configure warning that 'missing' script is too old or missing.
  (Reported by Floren Munteanu. Github #33.)
• Previously nmake /f Makefile.vc clean would fail on Windows. This was
  fixed.
• Obsolete win32 and NetWare make files were removed.
• Numerous documentation updates. (Reported by Thomas Pöchtrager. GitHub #48.)