Add ColorIndexForNumber macro replacing '& 0x07'

Makes it easier to add more colors.

code/qcommon/q_shared.h

@@ -403,7 +403,8 @@ extern	vec4_t		colorDkGrey;
 #define COLOR_CYAN	'5'
 #define COLOR_MAGENTA	'6'
 #define COLOR_WHITE	'7'
-#define ColorIndex(c)	(((c) - '0') & 0x07)
+#define ColorIndexForNumber(c) ((c) & 0x07)
+#define ColorIndex(c) (ColorIndexForNumber((c) - '0'))
 
 #define S_COLOR_BLACK	"^0"
 #define S_COLOR_RED	"^1"