Add keyboard event handler to shell

shell.asm

@@ -94,13 +94,21 @@ process_event:
 	cmp al, WM_PAINT
 	jne .not_paint
 	call paint
+	jmp .end
 	.not_paint:
 
 	cmp al, WM_MOUSE
 	jne .not_mouse
 	call mouse
+	jmp .end
 	.not_mouse:
 
+	cmp al, WM_KEYBOARD
+	jne .not_keyboard
+	call keyboard
+	.not_keyboard
+
+	.end:
 	pop es
 	pop ds
 	pop bp
@@ -181,6 +189,14 @@ mouse:
 		call forward_event
 		ret
 
+keyboard:
+	call get_window
+	mov si, [si + window.data]
+	add si, 20
+	mov [si], cl
+	call request_redraw
+	ret
+
 ; in:
 ;  bx = valid window id for this process
 ; out: