Add save and restore of each pin used in reading joystick (AVR).

Allow output pin to be JS_VIRTUAL_AXIS if the axis is connected to Vcc
instead of an output pin from the MCU.

Fix joystick report id

Fix broken v-usb hid joystick interface. Make it more resilient to unusual settings (none multiple of eight button count, 0 buttons or 0 axes)

Correct adc reading for multiple axes. Piecewise range conversion for uncentered raw value range. Input, output and ground pin configuration per axis.

Documentation fixes

quantum/joystick.c

@@ -2,7 +2,11 @@
 
 joystick_t joystick_status = { 
   .buttons = {0},
-  .axes = {0},
+  .axes = {
+#if JOYSTICK_AXES_COUNT>0
+  0
+#endif
+    },
   .status = 0
 };