add support for hid gamepad interface

add documentation for HID joystick
Add joystick_task to read analog axes values even when no key is pressed or release. update doc
Update docs/feature_joystick.md
Manage pin setup and read to maintain matrix scan after analog read

docs/_summary.md

@@ -97,6 +97,7 @@
     * [DIP Switch](feature_dip_switch.md)
     * [Encoders](feature_encoders.md)
     * [Haptic Feedback](feature_haptic_feedback.md)
+    * [Joystick](feature_joystick.md)
     * [Proton C Conversion](proton_c_conversion.md)
     * [PS/2 Mouse](feature_ps2_mouse.md)
     * [Split Keyboard](feature_split_keyboard.md)

docs/feature_joystick.md

@@ -0,0 +1,85 @@
+## Joystick HID Device
+
+The keyboard can be made to be recognized as a joystick HID device by the Operating System. 
+
+This is enabled by adding the following to `rules.mk`
+
+```
+JOYSTICK_ENABLE = yes
+```
+
+### Configuring the joystick
+
+The default joystick has 2 axes and and 8 buttons. This can be changed from the config.h file : 
+
+```
+//max 32 for JOYSTICK_BUTTON_COUNT
+#define JOYSTICK_BUTTON_COUNT 16
+//max 6 for JOYSTICK_AXES_COUNT
+#define JOYSTICK_AXES_COUNT 3
+```
+
+When defining axes for your joystick, you have to provide a definition array for it. You can do this from your keymap.c file.
+A joystick will either be read from an input pin that allows the use of an ADC, or can be virtual, so that its value is provided by your code.
+You have to define an array of type ''joystick_config_t'' and of proper size, in the following way : 
+
+```
+//joystick config
+joystick_config_t joystick_axes[JOYSTICK_AXES_COUNT] = {
+  [0] = {A1, D7, 65280, 65472},
+  [1] = {JS_VIRTUAL_AXIS, JS_VIRTUAL_AXIS, 65280, 65472}
+};
+```
+
+In this example, the first axis will be read from the D7 pin while A1 is set high, using an analogRead, whereas the second axis will not be read. 
+If you connected the your analog component to Vcc instead of an output pin, you can set the output setting to JS_VIRTUAL_AXIS.
+In order to give a value to the second axis, you can do so in any customizable entry point of quantum : as an action, in process_record_user or in matrix_scan_user, or even in joystick_task(void) which is called even when no key has been pressed.
+You assign a value by writing to joystick_status.axes[axis_index] a signed 8bit value (-127 to 127). Then it is necessary to assign the flag JS_UPDATED to joystick_status.status in order for the change to be taken into account.
+
+The following example writes two axes based on keypad presses, with KP_5 as a precision modifier : 
+
+```
+#ifdef JOYSTICK_ENABLE
+static bool precision_on;
+#endif
+
+bool process_record_user(uint16_t keycode, keyrecord_t *record) {
+  switch(keycode){
+#ifdef JOYSTICK_ENABLE
+    // virtual joystick
+    case KC_P8:
+      joystick_status.axes[1] -= (record->event.pressed ? 1 : -1) * (precision_on ?70 : 127);
+      joystick_status.status |= JS_UPDATED;
+    break;
+    case KC_P2:
+      joystick_status.axes[1] += (record->event.pressed ? 1 : -1) * (precision_on ?70 : 127);
+      joystick_status.status |= JS_UPDATED;
+    break;
+    case KC_P4:
+      joystick_status.axes[0] -= (record->event.pressed ? 1 : -1) * (precision_on ?70 : 127);
+      joystick_status.status |= JS_UPDATED;
+    break;
+    case KC_P6:
+      joystick_status.axes[0] += (record->event.pressed ? 1 : -1) * (precision_on ?70 : 127);
+      joystick_status.status |= JS_UPDATED;
+    break;
+    case KC_P5:
+    precision_on = record->event.pressed;
+    joystick_status.axes[0] *= record->event.pressed ? 70/127.f : 127/70.f;
+    joystick_status.axes[1] *= record->event.pressed ? 70/127.f : 127/70.f;
+    joystick_status.status |= JS_UPDATED;
+    break;
+#endif
+  }
+  
+  return true;
+}
+```
+
+### Triggering joystick buttons
+
+Joystick buttons are normal quantum keycode, defined as JS_BUTTON0 to JS_BUTTON_MAX, which depends on the number of buttons you have configured.
+To trigger a joystick button, just add the corresponding keycode to your keymap.
+
+
+