Improve wxImage handlers documentation, especially ownership aspect.

Correct wxImage::RemoveHandler() documentation which was plain wrong.

Also mention that the handler will be deleted by wxImage in AddHandler()
documentation.

And add an example of using AddHandler() as well as fix the broken text in
wxInitAllImageHandlers() description.

Closes #12772.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66370 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/image.h

@@ -1556,7 +1556,19 @@ public:
 
     /**
         Register an image handler.
-        See @ref image_handlers for a list of the available handlers.
+
+        Typical example of use:
+        @code
+            wxImage::AddHandler(new wxPNGHandler);
+        @endcode
+
+        See @ref image_handlers for a list of the available handlers. You can
+        also use ::wxInitAllImageHandlers() to add handlers for all the image
+        formats supported by wxWidgets at once.
+
+        @param handler
+            A heap-allocated handler object which will be deleted by wxImage
+            if it is removed later by RemoveHandler() or at program shutdown.
     */
     static void AddHandler(wxImageHandler* handler);
 
@@ -1648,7 +1660,8 @@ public:
 
     /**
         Finds the handler with the given name, and removes it.
-        The handler is not deleted.
+
+        The handler is also deleted.
 
         @param name
             The handler name.
@@ -1760,9 +1773,14 @@ wxImage wxNullImage;
 //@{
 
 /**
-    Initializes all available image handlers. For a list of available handlers,
-    see wxImage.
-    If you don't need/want all image handlers loaded
+    Initializes all available image handlers.
+
+    This function call wxImage::AddHandler() for all the available image
+    handlers (see @ref image_handlers for the full list). Calling it is the
+    simplest way to initialize wxImage but it creates and registers even the
+    handlers your program may not use. If you want to avoid the overhead of
+    doing this you need to call wxImage::AddHandler() manually just for the
+    handlers that you do want to use.
 
     @see wxImage, wxImageHandler