nes: Expose and document all joypad keys

include/nes.h

@@ -90,6 +90,15 @@
 /* No support for dynamically loadable drivers */
 #define DYN_DRV         0
 
+/* The joystick keys - all keys are supported */
+#define KEY_UP		0x10
+#define KEY_DOWN	0x20
+#define KEY_LEFT	0x40
+#define KEY_RIGHT	0x80
+#define KEY_A		0x1
+#define KEY_B		0x2
+#define KEY_SELECT	0x4
+#define KEY_START	0x8
 
 
 /* The addresses of the static drivers */