fix wxWindow::PushEventHandler and related wxWindow functions for the stack management; currently they don't work well when passing event handlers which are part of an event handler chain (see wx-dev thread 'wxWindow event handler stack'); implement wxEvtHandler Unlink() and IsUnlinked() functions and document them; revise docs of all involved functions of both wxEvtHandler and wxWindow, adding images for better explanations

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58291 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/wxwidgets.css

@@ -283,7 +283,7 @@ HR {
 }
 
 .memproto, .memdoc {
-	border: 1px solid #84b0c7;	
+	border: 1px solid #84b0c7;
 }
 
 .memproto {
@@ -400,6 +400,10 @@ H2 > A.anchor {
 	color: black;
 }
 
+IMG {
+    margin: 20px;
+}
+
 IMG.logo {
 	float: right;
 	margin: 20px;