Add support for USB mice.

Initial support for USB mice that follow the "boot" protocol.
diff --git a/src/usb-hid.h b/src/usb-hid.h
index 6af4da2..d8199b9 100644
--- a/src/usb-hid.h
+++ b/src/usb-hid.h
@@ -4,12 +4,14 @@
 // usb-hid.c
 struct usb_interface_descriptor;
 struct usb_pipe;
-int usb_keyboard_init(struct usb_pipe *pipe
-                      , struct usb_interface_descriptor *iface, int imax);
-void usb_keyboard_setup(void);
+int usb_hid_init(struct usb_pipe *pipe
+                 , struct usb_interface_descriptor *iface, int imax);
+void usb_hid_setup(void);
 inline int usb_kbd_active(void);
-void usb_check_key(void);
 inline int usb_kbd_command(int command, u8 *param);
+inline int usb_mouse_active(void);
+inline int usb_mouse_command(int command, u8 *param);
+void usb_check_event(void);
 
 
 /****************************************************************