win32tty keystroke handling

- Move the code for keystroke handling into its own source file.
- Compile and link it as a dynamic link library.
- Dynamically load the keystroke handler at runtime
- Add support for specifying a different handler in defaults.nh
  so that internationalization issues can be dealt with without
  rebuilding nethack, just supply alternative handlers in HACKDIR.

The following exported functions need to be present in
the keystroke handler .dll:
ProcessKeystroke - returns an ascii value to NetHack
NHkbhit  - allows peeking to see if a key/mouse press is waiting
SourceWhere - returns location for souce code for a keystroke handler
SourceAuthor  - returns author information for a keystroke handler
KeyHandlerName  - returns the full or short name of the keystroke handling dll.

Files

@@ -190,8 +190,9 @@ winmain.c
 sys/winnt:
 (files for Windows 9x, NT and Windows2000 version)
 Install.nt      Makefile.bcc    Makefile.gcc    Makefile.msc    console.rc
-defaults.nh     mapimail.c      nethack.def     nhico.uu        nhsetup.bat
-ntsound.c       nttty.c         porthelp        win32api.h      winnt.c
+defaults.nh     mapimail.c      nethack.def     nhdefkey.c      nhico.uu
+nhsetup.bat     ntsound.c       nttty.c         porthelp        win32api.h
+winnt.c
 
 util:
 (files for all versions)