Reset all handlers. This allowing to use same server few times (#93)

* Reset all handlers. This allowing to use same server few times during app life.
E.g. for WiFi manager when hardware sepups WiFi connection and as HTTP server during hardware life cycle

src/ESPAsyncWebServer.h

@@ -379,11 +379,13 @@ class AsyncWebServer {
 #endif
 
     AsyncWebRewrite& addRewrite(AsyncWebRewrite* rewrite);
-
+    bool removeRewrite(AsyncWebRewrite* rewrite);
+  
     AsyncWebRewrite& rewrite(const char* from, const char* to);
 
     AsyncWebHandler& addHandler(AsyncWebHandler* handler);
-
+    bool removeHandler(AsyncWebHandler* handler);
+  
     AsyncCallbackWebHandler& on(const char* uri, ArRequestHandlerFunction onRequest);
     AsyncCallbackWebHandler& on(const char* uri, WebRequestMethodComposite method, ArRequestHandlerFunction onRequest);
     AsyncCallbackWebHandler& on(const char* uri, WebRequestMethodComposite method, ArRequestHandlerFunction onRequest, ArUploadHandlerFunction onUpload);
@@ -395,6 +397,8 @@ class AsyncWebServer {
     void onFileUpload(ArUploadHandlerFunction fn); //handle file uploads
     void onRequestBody(ArBodyHandlerFunction fn); //handle posts with plain body content (JSON often transmitted this way as a request)
 
+    void reset(); //remove all writers and handlers, with onNotFound/onFileUpload/onRequestBody 
+  
     void _handleDisconnect(AsyncWebServerRequest *request);
     void _attachHandler(AsyncWebServerRequest *request);
     void _rewriteRequest(AsyncWebServerRequest *request);