v1.2.0 to save heap when sending large data

### Release v1.2.0

1. Support using `CString` to save heap to send `very large data`. Check [request->send(200, textPlainStr, jsonChartDataCharStr); - Without using String Class - to save heap #8](khoih-prog/Portenta_H7_AsyncWebServer#8)
2. Add multiple examples to demo the new feature

examples/MQTT_ThingStream/MQTT_ThingStream.ino

@@ -178,7 +178,7 @@ void setup()
 {
   // Open serial communications and wait for port to open:
   Serial.begin(115200);
-  while (!Serial);
+  while (!Serial && millis() < 5000);
 
   Serial.print("\nStart MQTT_ThingStream on "); Serial.print(BOARD_NAME);
   Serial.print(" with "); Serial.println(SHIELD_TYPE);

examples/WebClient/WebClient.ino

@@ -48,7 +48,7 @@ void setup()
 {
   // Open serial communications and wait for port to open:
   Serial.begin(115200);
-  while (!Serial);
+  while (!Serial && millis() < 5000);
 
   Serial.print("\nStart WebClient on "); Serial.print(BOARD_NAME);
   Serial.print(" with "); Serial.println(SHIELD_TYPE);

examples/WebClientRepeating/WebClientRepeating.ino

@@ -81,7 +81,7 @@ void setup()
 {
   // Open serial communications and wait for port to open:
   Serial.begin(115200);
-  while (!Serial);
+  while (!Serial && millis() < 5000);
 
   Serial.print("\nStart WebClientRepeating on "); Serial.print(BOARD_NAME);
   Serial.print(" with "); Serial.println(SHIELD_TYPE);