Added emscripten_remove_callback to doc

Author: ypujante

site/source/docs/api_reference/html5.h.rst

@@ -90,6 +90,50 @@ The ``useCapture`` parameter  maps to ``useCapture`` in `EventTarget.addEventLis
 
 Most functions return the result using the type :c:data:`EMSCRIPTEN_RESULT`. Zero and positive values denote success. Negative values signal failure. None of the functions fail or abort by throwing a JavaScript or C++ exception. If a particular browser does not support the given feature, the value :c:data:`EMSCRIPTEN_RESULT_NOT_SUPPORTED` will be returned at the time the callback is registered.
 
+Remove callback function
+------------------------
+
+In order to remove a callback, previously set via a ``emscripten_set_some_callback`` call, there is a dedicated and generic function for this purpose:
+
+  .. code-block:: cpp
+
+    EMSCRIPTEN_RESULT emscripten_remove_callback(
+      const char *target,   // ID of the target HTML element.
+      void *userData,       // User-defined data (passed to the callback).
+      int eventTypeId,      // The event type ID (EMSCRIPTEN_EVENT_XXX).
+      void *callback        // Callback function.
+    );
+
+
+The ``target``, ``userData`` and ``callback`` parameters are the same parameters provided in ``emscripten_set_some_callback`` with the only difference being that, since this function applies to all types of callbacks, the type of ``callback`` is ``void *``.
+
+The ``eventTypeId`` represents the event type, the same Id received in the callback functions.
+
+  .. code-block:: cpp
+
+    // Example
+
+    bool my_mouse_callback_1(int eventType, const EmscriptenMouseEvent *mouseEvent, void *userData) {
+      // ...
+    }
+
+    bool my_mouse_callback_2(int eventType, const EmscriptenMouseEvent *mouseEvent, void *userData) {
+      // ...
+    }
+
+    void main() {
+
+      // 1. set callbacks for mouse down and mouse move
+      emscripten_set_mousedown_callback("#mydiv", 0, my_mouse_callback_1);
+      emscripten_set_mousedown_callback("#mydiv", (void *) 34, my_mouse_callback_2);
+      emscripten_set_mousemove_callback("#mydiv", 0, my_mouse_callback_1);
+
+      // 2. remove these callbacks
+      emscripten_remove_callback("#mydiv", 0, EMSCRIPTEN_EVENT_MOUSEDOWN, my_mouse_callback_1);
+      emscripten_remove_callback("#mydiv", (void *) 34, EMSCRIPTEN_EVENT_MOUSEDOWN, my_mouse_callback_2);
+      emscripten_remove_callback("#mydiv", 0, EMSCRIPTEN_EVENT_MOUSEMOVE, my_mouse_callback_1);
+    }
+
 
 Callback functions
 ------------------