refactor keyboard scanner somewhat, and have no variables in ROM(!)

c64/kernal/irq_handler.s

@@ -27,5 +27,14 @@ default_irq_handler:
 
 	jsr blink_cursor
 	jsr scan_keyboard
+
+	lda KeyQuantity
+	sta $0400
+	lda Buffer+0
+	sta $0401
+	lda Buffer+1
+	sta $0402
+	lda Buffer+2
+	sta $0403
 	
 	jmp return_from_interrupt