Start on FILE i/O

inc/io.h

@@ -9,8 +9,9 @@
 #define SCREEN_ADDRESS 0
 #define KEYBOARD_ADDRESS 1
 #define ROM_BANKED_OUT 2
-
-int putChar(uint8_t c);
-int getChar(void);
+#define FILE_COMMAND 3
+#define FILE_DESCRIPTOR 4
+#define FILE_DATA 5 // two bytes, for pointer to string
+#define FILE_STATUS 7
 
 #endif // IO_H