Add Mouse horizontal scroll (thanks Xenoamor)

https://forum.pjrc.com/threads/33017-Teensy-3-1-Mouse-horizontal-scroll

teensy3/usb_desc.c

 static uint8_t device_descriptor[] = {
         18,                                     // bLength
         1,                                      // bDescriptorType
-        0x00, 0x02,                             // bcdUSB
+        0x01, 0x01,                             // bcdUSB
 #ifdef DEVICE_CLASS
         DEVICE_CLASS,                           // bDeviceClass
 #else
         0x75, 0x08,                     //   Report Size (8),
         0x95, 0x03,                     //   Report Count (3),
         0x81, 0x06,                     //   Input (Data, Variable, Relative)
+        0x05, 0x0C,                     //   Usage Page (Consumer)
+        0x0A, 0x38, 0x02,               //   Usage (AC Pan)
+        0x15, 0x81,                     //   Logical Minimum (-127)
+        0x25, 0x7F,                     //   Logical Maximum (127)
+        0x75, 0x08,                     //   Report Size (8),
+        0x95, 0x01,                     //   Report Count (1),
+        0x81, 0x06,                     //   Input (Data, Variable, Relative)
         0xC0,                           // End Collection
         0x05, 0x01,                     // Usage Page (Generic Desktop)
         0x09, 0x02,                     // Usage (Mouse)

teensy3/usb_mouse.c

         if (back) mask    |= 8;
         if (forward) mask |= 16;
         usb_mouse_buttons_state = mask;
-        return usb_mouse_move(0, 0, 0);
+        return usb_mouse_move(0, 0, 0, 0);
 }
 
 
 
 
 // Move the mouse.  x, y and wheel are -127 to 127.  Use 0 for no movement.
-int usb_mouse_move(int8_t x, int8_t y, int8_t wheel)
+int usb_mouse_move(int8_t x, int8_t y, int8_t wheel, int8_t horiz)
 {
         uint32_t wait_count=0;
         usb_packet_t *tx_packet;
         if (x == -128) x = -127;
         if (y == -128) y = -127;
         if (wheel == -128) wheel = -127;
+        if (horiz == -128) horiz = -127;
 
         while (1) {
                 if (!usb_configuration) {
         *(tx_packet->buf + 2) = x;
         *(tx_packet->buf + 3) = y;
         *(tx_packet->buf + 4) = wheel;
-        tx_packet->len = 5;
+        *(tx_packet->buf + 5) = horiz; // horizontal scroll
+        tx_packet->len = 6;
         usb_tx(MOUSE_ENDPOINT, tx_packet);
         return 0;
 }

teensy3/usb_mouse.h

 extern "C" {
 #endif
 int usb_mouse_buttons(uint8_t left, uint8_t middle, uint8_t right, uint8_t back, uint8_t forward);
-int usb_mouse_move(int8_t x, int8_t y, int8_t wheel);
+int usb_mouse_move(int8_t x, int8_t y, int8_t wheel, int8_t horiz);
 int usb_mouse_position(uint16_t x, uint16_t y);
 void usb_mouse_screen_size(uint16_t width, uint16_t height, uint8_t mac);
 extern uint8_t usb_mouse_buttons_state;
         public:
         void begin(void) { }
         void end(void) { }
-        void move(int8_t x, int8_t y, int8_t wheel=0) { usb_mouse_move(x, y, wheel); }
+        void move(int8_t x, int8_t y, int8_t wheel=0, int8_t horiz=0) {
+		usb_mouse_move(x, y, wheel, horiz);
+	}
 	void moveTo(uint16_t x, uint16_t y) { usb_mouse_position(x, y); }
 	void screenSize(uint16_t width, uint16_t height, bool isMacintosh = false) {
 		usb_mouse_screen_size(width, height, isMacintosh ? 1 : 0);
 	}
         void click(uint8_t b = MOUSE_LEFT) {
 		usb_mouse_buttons_state = b;
-		usb_mouse_move(0, 0, 0);
+		usb_mouse_move(0, 0, 0, 0);
 		usb_mouse_buttons_state = 0;
-		usb_mouse_move(0, 0, 0);
+		usb_mouse_move(0, 0, 0, 0);
 	}
-        void scroll(int8_t wheel) { usb_mouse_move(0, 0, wheel); }
+        void scroll(int8_t wheel, int8_t horiz=0) { usb_mouse_move(0, 0, wheel, horiz); }
         void set_buttons(uint8_t left, uint8_t middle=0, uint8_t right=0, uint8_t back=0, uint8_t forward=0) {
 		usb_mouse_buttons(left, middle, right, back, forward);
 	}
 		uint8_t buttons = usb_mouse_buttons_state | (b & MOUSE_ALL);
 		if (buttons != usb_mouse_buttons_state) {
 			usb_mouse_buttons_state = buttons;
-			usb_mouse_move(0, 0, 0);
+			usb_mouse_move(0, 0, 0, 0);
 		}
 	}
         void release(uint8_t b = MOUSE_LEFT) {
 		uint8_t buttons = usb_mouse_buttons_state & ~(b & MOUSE_ALL);
 		if (buttons != usb_mouse_buttons_state) {
 			usb_mouse_buttons_state = buttons;
-			usb_mouse_move(0, 0, 0);
+			usb_mouse_move(0, 0, 0, 0);
 		}
 	}
         bool isPressed(uint8_t b = MOUSE_ALL) {