v1.4.1 for core ESP8266 v3.0.2

### Releases v1.4.1

1. Examples modified and tested with core v3.0.2
2. Add instructions in `README.md`
3. Add `changelog.md`
4. Delete Blynk-related examples

Author: khoih-prog

CONTRIBUTING.md

@@ -14,8 +14,8 @@ If you don't find anything, please [open a new issue](https://github.com/khoih-p
 
 Please ensure to specify the following:
 
-* Arduino IDE version (e.g. 1.8.15) or Platform.io version
-* `ESP8266` Core Version (e.g. ESP8266 core v3.0.0)
+* Arduino IDE version (e.g. 1.8.16) or Platform.io version
+* `ESP8266` Core Version (e.g. ESP8266 core v3.0.2)
 * Contextual information (e.g. what you were trying to achieve)
 * Simplest possible steps to reproduce
 * Anything that might be relevant in your opinion, such as:
@@ -26,11 +26,11 @@ Please ensure to specify the following:
 ### Example
 
 ```
-Arduino IDE version: v1.8.15
-ESP8266 Core Version v3.0.0
+Arduino IDE version: v1.8.16
+ESP8266 Core Version v3.0.2
 ESP8266_NODEMCU
 OS: Ubuntu 20.04 LTS
-Linux xy-Inspiron-3593 5.4.0-73-generic #82-Ubuntu SMP Wed Apr 14 17:39:42 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
+Linux xy-Inspiron-3593 5.4.0-90-generic #101-Ubuntu SMP Fri Oct 15 20:00:55 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
 
 Context:
 I encountered a crash while trying to use the Timer Interrupt.