Change menu_headings to accept color and attribute

Instead of just accepting an attribute, it's now possible to
use a color, or both color and attribute, for example:

OPTIONS=menu_headings:inverse
OPTIONS=menu_headings:red
OPTIONS=menu_headings:red&underline

Default is still just inverse.
This lets the player change the menu heading color without
needing to use menu colors for them.

Also makes it so the core uses NO_COLOR instead of 0, for all
the menu lines which don't have any prefedefined color.

Tested for tty, curses, x11, qt, and win32

win/curses/cursmesg.c

@@ -488,7 +488,7 @@ curses_prev_mesg(void)
     boolean do_lifo = (iflags.prevmsg_window != 'f');
 #ifdef DEBUG
     static int showturn = 0; /* 1: show hero_seq value in separators */
-    int clr = 0;
+    int clr = NO_COLOR;
 
     /*
      * Set DEBUGFILES=MesgTurn in environment or sysconf to decorate