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

include/flag.h

@@ -186,6 +186,10 @@ struct debug_flags {
 #endif
 };
 
+typedef struct color_and_attr {
+    int color, attr;
+} color_attr;
+
 /*
  * Stuff that really isn't option or platform related and does not
  * get saved and restored.  They are set and cleared during the game
@@ -251,7 +255,7 @@ struct instance_flags {
     int getpos_coords;    /* show coordinates when getting cursor position */
     int menuinvertmode;  /* 0 = invert toggles every item;
                             1 = invert skips 'all items' item */
-    int menu_headings;    /* ATR for menu headings */
+    color_attr menu_headings;    /* ATR for menu headings */
     uint32_t colorcount;    /* store how many colors terminal is capable of */
     boolean use_truecolor;  /* force use of truecolor */
 #ifdef ALTMETA