v1.8.0 to fix multiple-definitions linker error

### Releases v1.8.0

1. Fix `multiple-definitions` linker error. Drop `src_cpp` and `src_h` directories
2. Add example `Argument_Complex_Multi` to demonstrate how to avoid `multiple-definitions` linker error in multiple-file projects

Author: khoih-prog

README.md

@@ -133,7 +133,7 @@ The catch is your function is now part of an ISR (Interrupt Service Routine), an
 
 ## Prerequisites
 
-1. [`Arduino IDE 1.8.16+` for Arduino](https://www.arduino.cc/en/Main/Software)
+1. [`Arduino IDE 1.8.19+` for Arduino](https://github.com/arduino/Arduino). [![GitHub release](https://img.shields.io/github/release/arduino/Arduino.svg)](https://github.com/arduino/Arduino/releases/latest)
 2. [`Arduino AVR core 1.8.3+`](https://github.com/arduino/ArduinoCore-avr) for Arduino AVR boards. Use Arduino Board Manager to install. [![Latest release](https://img.shields.io/github/release/arduino/ArduinoCore-avr.svg)](https://github.com/arduino/ArduinoCore-avr/releases/latest/)
 3. [`Adafruit AVR core 1.4.14+`](https://github.com/adafruit/Adafruit_Arduino_Boards) for Adafruit AVR boards. Use Arduino Board Manager to install. 
 4. [`Sparkfun AVR core 1.1.13+`](https://github.com/sparkfun/Arduino_Boards) for Sparkfun AVR boards. Use Arduino Board Manager to install.