add an interface for sound libraries

Groundwork for a more versatile interface for using
sound libraries. A lot of sound libraries work across
multiple platforms.

The current NetHack sound stuff is quite limited.

Binaries can have a variety of window ports linked into
them, and it makes sense to have something similar for
sound.

This tries to set things up in a more soundlib-centric way,
rather than inserting things in a platform-centric way.

It establishes a new top-level directory sound (akin to win
for the window interface routines, or "window-port") where
sound-related additions and sndprocs and support files can be
added and used across platforms.

The default interface is nosound and the 'nosound' interface
is in src/sounds.c

The interface for 'windsound', which contains the same minimal
USER_SOUNDS support using built-in routines that has been in the
windows port for a long time is added to
sound/windsound/windsound.c.

For now, the sound interface support for 'qtsound' has been added
to the existing Qt files win/Qt/qt_bind.h and win/Qt/qt_bind.cpp,
and a note has been placed in sound/qtsound/README.md to avoid
confusion.

New header file added: include/sndprocs.h.

include/winprocs.h

@@ -276,16 +276,6 @@ extern
 #define MAP_MODE_ASCII_FIT_TO_SCREEN 10
 #define MAP_MODE_TILES_FIT_TO_SCREEN 11
 
-#if 0
-#define WC_SND_SOUND   0x0001L /* 01 Port has some sound capabilities     */
-#define WC_SND_SPEAKER 0x0002L /* 02 Sound supported via built-in speaker */
-#define WC_SND_STEREO  0x0004L /* 03 Stereo sound supported               */
-#define WC_SND_RAW     0x0008L /* 04 Raw sound supported                  */
-#define WC_SND_WAVE    0x0010L /* 05 Wave support                         */
-#define WC_SND_MIDI    0x0020L /* 06 Midi support                         */
-                               /* 26 free bits */
-#endif
-
 struct wc_Opt {
     const char *wc_name;
     unsigned long wc_bit;