take initial stab at macsound interface

Use macOS AppKit framework routines for a first cut at a
macsound soundlib interface.

Requires WANT_MACSOUND=1 on build.

Nothing has been done to move the stock sounds into the resources
of a bundle, so after building, if you want to try the stock sounds
out:
	cp sound/wav/*.wav ~/Library/Sounds

Because the NSSound macOS routines always do the search, supposedly
the following locations are searched in this order:
   1. the application’s main bundle
   2. ~/Library/Sounds
   3. /Library/Sounds
   4. /Network/Library/Sounds
   5. /System/Library/Sounds

Although not specifically implemented as of yet, it may be pretty
close to being able to put soundeffects wav files (by se_ name)
into ~/Library/Sounds working for the SND_SOUNDEFFECTS_AUTOMAP feature.

Feedback is welcome. Contributions for improving it are even more
welcome.

The new soundlib supporting file is named
sound/macsound/macsound.m since it's got objective C in it.

Known bugs and glitches:

The Hero_playnotes on a set of 5 notes goes too fast, so there
needs to be a slight delay added between the note of a multi-note
play.

include/extern.h

@@ -2469,9 +2469,11 @@ extern void freedynamicdata(void);
 extern void store_savefileinfo(NHFILE *);
 extern void store_savefileinfo(NHFILE *);
 extern int nhdatatypes_size(void);
+#if 0
 extern void assignlog(char *, char*, int);
 extern FILE *getlog(NHFILE *);
 extern void closelog(NHFILE *);
+#endif
 
 /* ### sfstruct.c ### */